pg_stat_statements: Remove unnecessary call to GetUserId()

The same is done a couple of lines above, so there is no need for the
same, extra, call.

Author: Dong Wook Lee
Reviewed-by: Julien Rouhaud
Discussion: https://postgr.es/m/CAAcBya+szDd1Y6dJU4_dbH_Ye3=G=8O1oQGG01kv3Tpie7wELQ@mail.gmail.com

Author: michaelpq

contrib/pg_stat_statements/pg_stat_statements.c

@@ -1508,7 +1508,7 @@ pg_stat_statements_internal(FunctionCallInfo fcinfo,
 	pgssEntry  *entry;
 
 	/* Superusers or members of pg_read_all_stats members are allowed */
-	is_allowed_role = is_member_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS);
+	is_allowed_role = is_member_of_role(userid, ROLE_PG_READ_ALL_STATS);
 
 	/* hash table must exist already */
 	if (!pgss || !pgss_hash)