PG-203: Fix memory leak.

The query_txt variable is allocated at the beginning of the
pg_stat_monitor_internal() function and released at the end, but an
extra malloc call to allocate it was added within an internal loop in
the funcion, thus allocating memory for every loop iteration, without
releasing the memory in the loop.

The query_txt variable can be reused inside the loop body, so this
commit removes the redundant declaration of query_txt from inside the
loop, which also fixes the leak.

pg_stat_monitor.c

@@ -1546,7 +1546,6 @@ pg_stat_monitor_internal(FunctionCallInfo fcinfo,
 		uint64        planid = entry->key.planid;
 		uint64        appid = entry->key.appid;
 		unsigned char *buf = pgss_qbuf[bucketid];
-		char 		  *query_txt = (char*) malloc(PGSM_QUERY_MAX_LEN);
 #if PG_VERSION_NUM < 140000
 		bool 		  is_allowed_role = is_member_of_role(GetUserId(), DEFAULT_ROLE_READ_ALL_STATS);
 #else