Remove obsolete comment in pg_stat_statements.

Commit 76db9cb63 removed the use of multiple nesting counters,
but missed one comment describing that arrangement.

Back-patch to v17 where 76db9cb63 came in, just to avoid confusion.

Julien Rouhaud

Discussion: https://postgr.es/m/gfcwh3zjxc2vygltapgo7g6yacdor5s4ynr234b6v2ohhuvt7m@gr42joxalenw

contrib/pg_stat_statements/pg_stat_statements.c

@@ -886,13 +886,6 @@ pgss_planner(Query *parse,
 	 * We can't process the query if no query_string is provided, as
 	 * pgss_store needs it.  We also ignore query without queryid, as it would
 	 * be treated as a utility statement, which may not be the case.
-	 *
-	 * Note that planner_hook can be called from the planner itself, so we
-	 * have a specific nesting level for the planner.  However, utility
-	 * commands containing optimizable statements can also call the planner,
-	 * same for regular DML (for instance for underlying foreign key queries).
-	 * So testing the planner nesting level only is not enough to detect real
-	 * top level planner call.
 	 */
 	if (pgss_enabled(nesting_level)
 		&& pgss_track_planning && query_string