Remove leftover reference to old "flat file" mechanism in a comment.

hlinnaka · hlinnaka · commit 46012d152f8d · 2019-05-08T09:34:02.000+03:00
The flat file mechanism was removed in PostgreSQL 9.0.
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
@@ -4928,8 +4928,7 @@ xact_redo_abort(xl_xact_abort *xlrec, TransactionId xid)
 		ExpireTreeKnownAssignedTransactionIds(xid, xlrec->nsubxacts, sub_xids, max_xid);
 
 		/*
-		 * There are no flat files that need updating, nor invalidation
-		 * messages to send or undo.
+		 * There are no invalidation messages to send or undo.
 		 */
 
 		/*
