MINOR: contrib/prometheus-exporter: Remove usless rate metrics

Following metrics have been removed:

  * haproxy_frontend_connections_rate_current (ST_F_CONN_RATE)
  * haproxy_frontend_http_requests_rate_current (ST_F_REQ_RATE)
  * haproxy_*_current_session_rate (ST_F_RATE)

These rates can be deduced using the total value with this kind of formula:

  rate(haproxy_frontend_connections_total[1m])

No backport needed. See issue #81 on github.
diff --git a/contrib/prometheus-exporter/README b/contrib/prometheus-exporter/README
index f7fda6f..1fb5503 100644
--- a/contrib/prometheus-exporter/README
+++ b/contrib/prometheus-exporter/README
@@ -123,7 +123,6 @@
 | haproxy_frontend_max_sessions                   | Maximum observed number of active sessions.                                  |
 | haproxy_frontend_limit_sessions                 | Configured session limit.                                                    |
 | haproxy_frontend_sessions_total                 | Total number of sessions.                                                    |
-| haproxy_frontend_current_session_rate           | Current number of sessions per second over last elapsed second.              |
 | haproxy_frontend_limit_session_rate             | Configured limit on new sessions per second.                                 |
 | haproxy_frontend_max_session_rate               | Maximum observed number of sessions per second.                              |
 | haproxy_frontend_connections_rate_current       | Current number of connections per second over the last elapsed second.       |
@@ -137,7 +136,6 @@
 | haproxy_frontend_denied_connections_total       | Total number of requests denied by "tcp-request connection" rules.           |
 | haproxy_frontend_denied_sessions_total          | Total number of requests denied by "tcp-request session" rules.              |
 | haproxy_frontend_failed_header_rewriting_total  | Total number of failed header rewriting warnings.                            |
-| haproxy_frontend_http_requests_rate_current     | Current number of HTTP requests per second over last elapsed second.         |
 | haproxy_frontend_http_requests_rate_max         | Maximum observed number of HTTP requests per second.                         |
 | haproxy_frontend_http_requests_total            | Total number of HTTP requests received.                                      |
 | haproxy_frontend_http_responses_total           | Total number of HTTP responses.                                              |
@@ -160,7 +158,6 @@
 | haproxy_backend_max_sessions                        | Maximum observed number of active sessions.                              |
 | haproxy_backend_limit_sessions                      | Configured session limit.                                                |
 | haproxy_backend_sessions_total                      | Total number of sessions.                                                |
-| haproxy_backend_current_session_rate                | Current number of sessions per second over last elapsed second.          |
 | haproxy_backend_max_session_rate                    | Maximum observed number of sessions per second.                          |
 | haproxy_backend_last_session_seconds                | Number of seconds since last session assigned to server/backend.         |
 | haproxy_backend_current_queue                       | Current number of queued requests.                                       |
@@ -209,7 +206,6 @@
 | haproxy_server_max_sessions                        | Maximum observed number of active sessions.                               |
 | haproxy_server_limit_sessions                      | Configured session limit.                                                 |
 | haproxy_server_sessions_total                      | Total number of sessions.                                                 |
-| haproxy_server_current_session_rate                | Current number of sessions per second over last elapsed second.           |
 | haproxy_server_max_session_rate                    | Maximum observed number of sessions per second.                           |
 | haproxy_server_last_session_seconds                | Number of seconds since last session assigned to server/backend.          |
 | haproxy_server_current_queue                       | Current number of queued requests.                                        |
diff --git a/contrib/prometheus-exporter/service-prometheus.c b/contrib/prometheus-exporter/service-prometheus.c
index 63bf4e6..dd9128a 100644
--- a/contrib/prometheus-exporter/service-prometheus.c
+++ b/contrib/prometheus-exporter/service-prometheus.c
@@ -151,7 +151,7 @@
 	[ST_F_SCUR]           = ST_F_SMAX,
 	[ST_F_SMAX]           = ST_F_SLIM,
 	[ST_F_SLIM]           = ST_F_STOT,
-	[ST_F_STOT]           = ST_F_RATE,
+	[ST_F_STOT]           = ST_F_RATE_LIM,
 	[ST_F_BIN]            = ST_F_BOUT,
 	[ST_F_BOUT]           = ST_F_DREQ,
 	[ST_F_DREQ]           = ST_F_DRESP,
@@ -177,9 +177,9 @@
 	[ST_F_LBTOT]          = 0,
 	[ST_F_TRACKED]        = 0,
 	[ST_F_TYPE]           = 0,
-	[ST_F_RATE]           = ST_F_RATE_LIM,
+	[ST_F_RATE]           = 0,
 	[ST_F_RATE_LIM]       = ST_F_RATE_MAX,
-	[ST_F_RATE_MAX]       = ST_F_CONN_RATE,
+	[ST_F_RATE_MAX]       = ST_F_CONN_RATE_MAX,
 	[ST_F_CHECK_STATUS]   = 0,
 	[ST_F_CHECK_CODE]     = 0,
 	[ST_F_CHECK_DURATION] = 0,
@@ -190,7 +190,7 @@
 	[ST_F_HRSP_5XX]       = ST_F_HRSP_OTHER,
 	[ST_F_HRSP_OTHER]     = ST_F_INTERCEPTED,
 	[ST_F_HANAFAIL]       = 0,
-	[ST_F_REQ_RATE]       = ST_F_REQ_RATE_MAX,
+	[ST_F_REQ_RATE]       = 0,
 	[ST_F_REQ_RATE_MAX]   = ST_F_REQ_TOT,
 	[ST_F_REQ_TOT]        = ST_F_HRSP_1XX,
 	[ST_F_CLI_ABRT]       = 0,
@@ -221,13 +221,13 @@
 	[ST_F_COOKIE]         = 0,
 	[ST_F_MODE]           = 0,
 	[ST_F_ALGO]           = 0,
-	[ST_F_CONN_RATE]      = ST_F_CONN_RATE_MAX,
+	[ST_F_CONN_RATE]      = 0,
 	[ST_F_CONN_RATE_MAX]  = ST_F_CONN_TOT,
 	[ST_F_CONN_TOT]       = ST_F_BIN,
 	[ST_F_INTERCEPTED]    = ST_F_CACHE_LOOKUPS,
 	[ST_F_DCON]           = ST_F_DSES,
 	[ST_F_DSES]           = ST_F_WREW,
-	[ST_F_WREW]           = ST_F_REQ_RATE,
+	[ST_F_WREW]           = ST_F_REQ_RATE_MAX,
 	[ST_F_CONNECT]        = 0,
 	[ST_F_REUSE]          = 0,
 	[ST_F_CACHE_LOOKUPS]  = ST_F_CACHE_HITS,
@@ -244,7 +244,7 @@
 	[ST_F_SCUR]           = ST_F_SMAX,
 	[ST_F_SMAX]           = ST_F_SLIM,
 	[ST_F_SLIM]           = ST_F_STOT,
-	[ST_F_STOT]           = ST_F_RATE,
+	[ST_F_STOT]           = ST_F_RATE_MAX,
 	[ST_F_BIN]            = ST_F_BOUT,
 	[ST_F_BOUT]           = ST_F_QTIME,
 	[ST_F_DREQ]           = ST_F_DRESP,
@@ -270,7 +270,7 @@
 	[ST_F_LBTOT]          = ST_F_REQ_TOT,
 	[ST_F_TRACKED]        = 9,
 	[ST_F_TYPE]           = 0,
-	[ST_F_RATE]           = ST_F_RATE_MAX,
+	[ST_F_RATE]           = 0,
 	[ST_F_RATE_LIM]       = 0,
 	[ST_F_RATE_MAX]       = ST_F_LASTSESS,
 	[ST_F_CHECK_STATUS]   = 0,
@@ -337,7 +337,7 @@
 	[ST_F_SCUR]           = ST_F_SMAX,
 	[ST_F_SMAX]           = ST_F_SLIM,
 	[ST_F_SLIM]           = ST_F_STOT,
-	[ST_F_STOT]           = ST_F_RATE,
+	[ST_F_STOT]           = ST_F_RATE_MAX,
 	[ST_F_BIN]            = ST_F_BOUT,
 	[ST_F_BOUT]           = ST_F_QTIME,
 	[ST_F_DREQ]           = 0,
@@ -363,7 +363,7 @@
 	[ST_F_LBTOT]          = ST_F_HRSP_1XX,
 	[ST_F_TRACKED]        = 0,
 	[ST_F_TYPE]           = 0,
-	[ST_F_RATE]           = ST_F_RATE_MAX,
+	[ST_F_RATE]           = 0,
 	[ST_F_RATE_LIM]       = 0,
 	[ST_F_RATE_MAX]       = ST_F_LASTSESS,
 	[ST_F_CHECK_STATUS]   = 0,
@@ -987,7 +987,7 @@
 	[ST_F_LBTOT]          = IST("counter"),
 	[ST_F_TRACKED]        = IST("untyped"),
 	[ST_F_TYPE]           = IST("untyped"),
-	[ST_F_RATE]           = IST("gauge"),
+	[ST_F_RATE]           = IST("untyped"),
 	[ST_F_RATE_LIM]       = IST("gauge"),
 	[ST_F_RATE_MAX]       = IST("counter"),
 	[ST_F_CHECK_STATUS]   = IST("untyped"),
@@ -1000,7 +1000,7 @@
 	[ST_F_HRSP_5XX]       = IST("counter"),
 	[ST_F_HRSP_OTHER]     = IST("counter"),
 	[ST_F_HANAFAIL]       = IST("counter"),
-	[ST_F_REQ_RATE]       = IST("gauge"),
+	[ST_F_REQ_RATE]       = IST("untyped"),
 	[ST_F_REQ_RATE_MAX]   = IST("counter"),
 	[ST_F_REQ_TOT]        = IST("counter"),
 	[ST_F_CLI_ABRT]       = IST("counter"),
@@ -1031,7 +1031,7 @@
 	[ST_F_COOKIE]         = IST("untyped"),
 	[ST_F_MODE]           = IST("untyped"),
 	[ST_F_ALGO]           = IST("untyped"),
-	[ST_F_CONN_RATE]      = IST("gauge"),
+	[ST_F_CONN_RATE]      = IST("untyped"),
 	[ST_F_CONN_RATE_MAX]  = IST("counter"),
 	[ST_F_CONN_TOT]       = IST("counter"),
 	[ST_F_INTERCEPTED]    = IST("counter"),
@@ -1454,18 +1454,12 @@
 				case ST_F_STOT:
 					metric = mkf_u64(FN_COUNTER, px->fe_counters.cum_sess);
 					break;
-				case ST_F_RATE:
-					metric = mkf_u32(FN_RATE, read_freq_ctr(&px->fe_sess_per_sec));
-					break;
 				case ST_F_RATE_LIM:
 					metric = mkf_u32(FO_CONFIG|FN_LIMIT, px->fe_sps_lim);
 					break;
 				case ST_F_RATE_MAX:
 					metric = mkf_u32(FN_MAX, px->fe_counters.sps_max);
 					break;
-				case ST_F_CONN_RATE:
-					metric = mkf_u32(FN_RATE, read_freq_ctr(&px->fe_conn_per_sec));
-					break;
 				case ST_F_CONN_RATE_MAX:
 					metric = mkf_u32(FN_MAX, px->fe_counters.cps_max);
 					break;
@@ -1496,11 +1490,6 @@
 				case ST_F_WREW:
 					metric = mkf_u64(FN_COUNTER, px->fe_counters.failed_rewrites);
 					break;
-				case ST_F_REQ_RATE:
-					if (px->mode != PR_MODE_HTTP)
-						goto next_px;
-					metric = mkf_u32(FN_RATE, read_freq_ctr(&px->fe_req_per_sec));
-					break;
 				case ST_F_REQ_RATE_MAX:
 					if (px->mode != PR_MODE_HTTP)
 						goto next_px;
@@ -1644,9 +1633,6 @@
 				case ST_F_STOT:
 					metric = mkf_u64(FN_COUNTER, px->be_counters.cum_conn);
 					break;
-				case ST_F_RATE:
-					metric = mkf_u32(0, read_freq_ctr(&px->be_sess_per_sec));
-					break;
 				case ST_F_RATE_MAX:
 					metric = mkf_u32(0, px->be_counters.sps_max);
 					break;
@@ -1869,9 +1855,6 @@
 					case ST_F_STOT:
 						metric = mkf_u64(FN_COUNTER, sv->counters.cum_sess);
 						break;
-					case ST_F_RATE:
-						metric = mkf_u32(FN_RATE, read_freq_ctr(&sv->sess_per_sec));
-						break;
 					case ST_F_RATE_MAX:
 						metric = mkf_u32(FN_MAX, sv->counters.sps_max);
 						break;