Remove unused check in heap_xlog_insert()

8e03eb92e9 reverted the commit 39b66a91bd which allowed freezing
in the heap_insert() code path but forgot to remove the corresponding
check in heap_xlog_insert(). This code is extraneous but not harmful.
However, cleaning it up makes it very clear that, as of now, we do not
support any freezing of pages in the heap_insert() path.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: https://postgr.es/m/flat/CAAKRu_Zp4Pi-t51OFWm1YZ-cctDfBhHCMZ%3DEx6PKxv0o8y2GvA%40mail.gmail.com
Backpatch-through: 14

src/backend/access/heap/heapam.c

@@ -9569,6 +9569,9 @@ heap_xlog_insert(XLogReaderState *record)
 	ItemPointerSetBlockNumber(&target_tid, blkno);
 	ItemPointerSetOffsetNumber(&target_tid, xlrec->offnum);
 
+	/* No freezing in the heap_insert() code path */
+	Assert(!(xlrec->flags & XLH_INSERT_ALL_FROZEN_SET));
+
 	/*
 	 * The visibility map may need to be fixed even if the heap page is
 	 * already up-to-date.
@@ -9639,10 +9642,6 @@ heap_xlog_insert(XLogReaderState *record)
 		if (xlrec->flags & XLH_INSERT_ALL_VISIBLE_CLEARED)
 			PageClearAllVisible(page);
 
-		/* XLH_INSERT_ALL_FROZEN_SET implies that all tuples are visible */
-		if (xlrec->flags & XLH_INSERT_ALL_FROZEN_SET)
-			PageSetAllVisible(page);
-
 		MarkBufferDirty(buffer);
 	}
 	if (BufferIsValid(buffer))