BUG/MINOR: promex: Remove Help prefix repeated twice for each metric

When the support for modules was added, the function producing the #HELP
line of each metric was refactored. Since then, the prefix "#HELP
<metric-name>" is printed twice because a code block was not removed. It is
now fixed.

This patch must be backported to 3.0.

(cherry picked from commit b789cef)
Signed-off-by: Christopher Faulet <[email protected]>

Author: capflam

addons/promex/service-prometheus.c

@@ -438,11 +438,6 @@ static int promex_dump_ts_header(const struct ist name, const struct ist desc, e
 			t = ist("gauge");
 	}
 
-	if (istcat(out, ist("# HELP "), max) == -1 ||
-	    istcat(out, name, max) == -1 ||
-	    istcat(out, ist(" "), max) == -1)
-		goto full;
-
 	if (istcat(out, ist("# HELP "), max) == -1 ||
 	    istcat(out, name, max) == -1 ||
 	    istcat(out, ist(" "), max) == -1 ||