MAJOR: http: Remove the HTTP legacy code

First of all, all legacy HTTP analyzers and all functions exclusively used by
them were removed. So the most of the functions in proto_http.{c,h} were
removed. Only functions to deal with the HTTP transaction have been kept. Then,
http_msg and hdr_idx modules were entirely removed. And finally the structure
http_msg was lightened of all its useless information about the legacy HTTP. The
structure hdr_ctx was also removed because unused now, just like unused states
in the enum h1_state. Note that the memory pool "hdr_idx" was removed and
"http_txn" is now smaller.
diff --git a/src/tcp_rules.c b/src/tcp_rules.c
index d81ffe3..99af7c7 100644
--- a/src/tcp_rules.c
+++ b/src/tcp_rules.c
@@ -743,7 +743,7 @@
 		curpx->req_cap = hdr;
 		curpx->to_log |= LW_REQHDR;
 
-		/* check if we need to allocate an hdr_idx struct for HTTP parsing */
+		/* check if we need to allocate an http_txn struct for HTTP parsing */
 		curpx->http_needed |= !!(expr->fetch->use & SMP_USE_HTTP_ANY);
 
 		rule->arg.cap.expr = expr;
@@ -781,7 +781,7 @@
 			return -1;
 		}
 
-		/* check if we need to allocate an hdr_idx struct for HTTP parsing */
+		/* check if we need to allocate an http_txn struct for HTTP parsing */
 		curpx->http_needed |= !!(expr->fetch->use & SMP_USE_HTTP_ANY);
 
 		if (strcmp(args[arg], "table") == 0) {