MINOR: contrib/prometheus-exporter: Don't needlessly set empty label for metrics

There is no reason to define empty labels for metrics. By default, all labels
are initialized to an empty ist.
diff --git a/contrib/prometheus-exporter/service-prometheus.c b/contrib/prometheus-exporter/service-prometheus.c
index 92613e8..81f5ba0 100644
--- a/contrib/prometheus-exporter/service-prometheus.c
+++ b/contrib/prometheus-exporter/service-prometheus.c
@@ -750,169 +750,17 @@
 
 /* Specific labels for all info fields. Empty by default. */
 const struct ist promex_inf_metric_labels[INF_TOTAL_FIELDS] = {
-	[INF_NAME]                           = IST(""),
-	[INF_VERSION]                        = IST(""),
-	[INF_RELEASE_DATE]                   = IST(""),
-	[INF_BUILD_INFO]                     = IST(PROMEX_BUILDINFO_LABEL),
-	[INF_NBTHREAD]                       = IST(""),
-	[INF_NBPROC]                         = IST(""),
-	[INF_PROCESS_NUM]                    = IST(""),
-	[INF_PID]                            = IST(""),
-	[INF_UPTIME]                         = IST(""),
-	[INF_UPTIME_SEC]                     = IST(""),
-	[INF_START_TIME_SEC]                 = IST(""),
-	[INF_MEMMAX_BYTES]                   = IST(""),
-	[INF_POOL_ALLOC_BYTES]               = IST(""),
-	[INF_POOL_USED_BYTES]                = IST(""),
-	[INF_POOL_FAILED]                    = IST(""),
-	[INF_ULIMIT_N]                       = IST(""),
-	[INF_MAXSOCK]                        = IST(""),
-	[INF_MAXCONN]                        = IST(""),
-	[INF_HARD_MAXCONN]                   = IST(""),
-	[INF_CURR_CONN]                      = IST(""),
-	[INF_CUM_CONN]                       = IST(""),
-	[INF_CUM_REQ]                        = IST(""),
-	[INF_MAX_SSL_CONNS]                  = IST(""),
-	[INF_CURR_SSL_CONNS]                 = IST(""),
-	[INF_CUM_SSL_CONNS]                  = IST(""),
-	[INF_MAXPIPES]                       = IST(""),
-	[INF_PIPES_USED]                     = IST(""),
-	[INF_PIPES_FREE]                     = IST(""),
-	[INF_CONN_RATE]                      = IST(""),
-	[INF_CONN_RATE_LIMIT]                = IST(""),
-	[INF_MAX_CONN_RATE]                  = IST(""),
-	[INF_SESS_RATE]                      = IST(""),
-	[INF_SESS_RATE_LIMIT]                = IST(""),
-	[INF_MAX_SESS_RATE]                  = IST(""),
-	[INF_SSL_RATE]                       = IST(""),
-	[INF_SSL_RATE_LIMIT]                 = IST(""),
-	[INF_MAX_SSL_RATE]                   = IST(""),
-	[INF_SSL_FRONTEND_KEY_RATE]          = IST(""),
-	[INF_SSL_FRONTEND_MAX_KEY_RATE]      = IST(""),
-	[INF_SSL_FRONTEND_SESSION_REUSE_PCT] = IST(""),
-	[INF_SSL_BACKEND_KEY_RATE]           = IST(""),
-	[INF_SSL_BACKEND_MAX_KEY_RATE]       = IST(""),
-	[INF_SSL_CACHE_LOOKUPS]              = IST(""),
-	[INF_SSL_CACHE_MISSES]               = IST(""),
-	[INF_COMPRESS_BPS_IN]                = IST(""),
-	[INF_COMPRESS_BPS_OUT]               = IST(""),
-	[INF_COMPRESS_BPS_RATE_LIM]          = IST(""),
-	[INF_ZLIB_MEM_USAGE]                 = IST(""),
-	[INF_MAX_ZLIB_MEM_USAGE]             = IST(""),
-	[INF_TASKS]                          = IST(""),
-	[INF_RUN_QUEUE]                      = IST(""),
-	[INF_IDLE_PCT]                       = IST(""),
-	[INF_NODE]                           = IST(""),
-	[INF_DESCRIPTION]                    = IST(""),
-	[INF_STOPPING]                       = IST(""),
-	[INF_JOBS]                           = IST(""),
-	[INF_UNSTOPPABLE_JOBS]               = IST(""),
-	[INF_LISTENERS]                      = IST(""),
-	[INF_ACTIVE_PEERS]                   = IST(""),
-	[INF_CONNECTED_PEERS]                = IST(""),
-	[INF_DROPPED_LOGS]                   = IST(""),
-	[INF_BUSY_POLLING]                   = IST(""),
-	[INF_FAILED_RESOLUTIONS]             = IST(""),
-	[INF_TOTAL_BYTES_OUT]                = IST(""),
-	[INF_TOTAL_SPLICED_BYTES_OUT]        = IST(""),
-	[INF_BYTES_OUT_RATE]                 = IST(""),
-	[INF_DEBUG_COMMANDS_ISSUED]          = IST(""),
+	[INF_BUILD_INFO]  = IST(PROMEX_BUILDINFO_LABEL),
 };
 
 /* Specific labels for all stats fields. Empty by default. */
 const struct ist promex_st_metric_labels[ST_F_TOTAL_FIELDS] = {
-	[ST_F_PXNAME]         = IST(""),
-	[ST_F_SVNAME]         = IST(""),
-	[ST_F_QCUR]           = IST(""),
-	[ST_F_QMAX]           = IST(""),
-	[ST_F_SCUR]           = IST(""),
-	[ST_F_SMAX]           = IST(""),
-	[ST_F_SLIM]           = IST(""),
-	[ST_F_STOT]           = IST(""),
-	[ST_F_BIN]            = IST(""),
-	[ST_F_BOUT]           = IST(""),
-	[ST_F_DREQ]           = IST(""),
-	[ST_F_DRESP]          = IST(""),
-	[ST_F_EREQ]           = IST(""),
-	[ST_F_ECON]           = IST(""),
-	[ST_F_ERESP]          = IST(""),
-	[ST_F_WRETR]          = IST(""),
-	[ST_F_WREDIS]         = IST(""),
-	[ST_F_STATUS]         = IST(""),
-	[ST_F_WEIGHT]         = IST(""),
-	[ST_F_ACT]            = IST(""),
-	[ST_F_BCK]            = IST(""),
-	[ST_F_CHKFAIL]        = IST(""),
-	[ST_F_CHKDOWN]        = IST(""),
-	[ST_F_LASTCHG]        = IST(""),
-	[ST_F_DOWNTIME]       = IST(""),
-	[ST_F_QLIMIT]         = IST(""),
-	[ST_F_PID]            = IST(""),
-	[ST_F_IID]            = IST(""),
-	[ST_F_SID]            = IST(""),
-	[ST_F_THROTTLE]       = IST(""),
-	[ST_F_LBTOT]          = IST(""),
-	[ST_F_TRACKED]        = IST(""),
-	[ST_F_TYPE]           = IST(""),
-	[ST_F_RATE]           = IST(""),
-	[ST_F_RATE_LIM]       = IST(""),
-	[ST_F_RATE_MAX]       = IST(""),
-	[ST_F_CHECK_STATUS]   = IST(""),
-	[ST_F_CHECK_CODE]     = IST(""),
-	[ST_F_CHECK_DURATION] = IST(""),
-	[ST_F_HRSP_1XX]       = IST("code=\"1xx\""),
-	[ST_F_HRSP_2XX]       = IST("code=\"2xx\""),
-	[ST_F_HRSP_3XX]       = IST("code=\"3xx\""),
-	[ST_F_HRSP_4XX]       = IST("code=\"4xx\""),
-	[ST_F_HRSP_5XX]       = IST("code=\"5xx\""),
-	[ST_F_HRSP_OTHER]     = IST("code=\"other\""),
-	[ST_F_HANAFAIL]       = IST(""),
-	[ST_F_REQ_RATE]       = IST(""),
-	[ST_F_REQ_RATE_MAX]   = IST(""),
-	[ST_F_REQ_TOT]        = IST(""),
-	[ST_F_CLI_ABRT]       = IST(""),
-	[ST_F_SRV_ABRT]       = IST(""),
-	[ST_F_COMP_IN]        = IST(""),
-	[ST_F_COMP_OUT]       = IST(""),
-	[ST_F_COMP_BYP]       = IST(""),
-	[ST_F_COMP_RSP]       = IST(""),
-	[ST_F_LASTSESS]       = IST(""),
-	[ST_F_LAST_CHK]       = IST(""),
-	[ST_F_LAST_AGT]       = IST(""),
-	[ST_F_QTIME]          = IST(""),
-	[ST_F_CTIME]          = IST(""),
-	[ST_F_RTIME]          = IST(""),
-	[ST_F_TTIME]          = IST(""),
-	[ST_F_AGENT_STATUS]   = IST(""),
-	[ST_F_AGENT_CODE]     = IST(""),
-	[ST_F_AGENT_DURATION] = IST(""),
-	[ST_F_CHECK_DESC]     = IST(""),
-	[ST_F_AGENT_DESC]     = IST(""),
-	[ST_F_CHECK_RISE]     = IST(""),
-	[ST_F_CHECK_FALL]     = IST(""),
-	[ST_F_CHECK_HEALTH]   = IST(""),
-	[ST_F_AGENT_RISE]     = IST(""),
-	[ST_F_AGENT_FALL]     = IST(""),
-	[ST_F_AGENT_HEALTH]   = IST(""),
-	[ST_F_ADDR]           = IST(""),
-	[ST_F_COOKIE]         = IST(""),
-	[ST_F_MODE]           = IST(""),
-	[ST_F_ALGO]           = IST(""),
-	[ST_F_CONN_RATE]      = IST(""),
-	[ST_F_CONN_RATE_MAX]  = IST(""),
-	[ST_F_CONN_TOT]       = IST(""),
-	[ST_F_INTERCEPTED]    = IST(""),
-	[ST_F_DCON]           = IST(""),
-	[ST_F_DSES]           = IST(""),
-	[ST_F_WREW]           = IST(""),
-	[ST_F_CONNECT]        = IST(""),
-	[ST_F_REUSE]          = IST(""),
-	[ST_F_CACHE_LOOKUPS]  = IST(""),
-	[ST_F_CACHE_HITS]     = IST(""),
-	[ST_F_IDLE_CONN_CUR]  = IST(""),
-	[ST_F_SAFE_CONN_CUR]  = IST(""),
-	[ST_F_USED_CONN_CUR]  = IST(""),
-	[ST_F_NEED_CONN_EST]  = IST(""),
+	[ST_F_HRSP_1XX]   = IST("code=\"1xx\""),
+	[ST_F_HRSP_2XX]   = IST("code=\"2xx\""),
+	[ST_F_HRSP_3XX]   = IST("code=\"3xx\""),
+	[ST_F_HRSP_4XX]   = IST("code=\"4xx\""),
+	[ST_F_HRSP_5XX]   = IST("code=\"5xx\""),
+	[ST_F_HRSP_OTHER] = IST("code=\"other\""),
 };
 
 /* Type for all info fields. "untyped" is used for unsupported field. */