Fix some long-obsolete references to XLogOpenRelation.

These were missed in commit a213f1ee6c,
which removed that function.

src/backend/access/transam/README

@@ -481,8 +481,7 @@ rdata array, even if some of the rdata items point into the buffer.  This is
 because you don't want XLogInsert to log the whole page contents.  The
 standard replay-routine pattern for this case is
 
-	reln = XLogOpenRelation(rnode);
-	buffer = XLogReadBuffer(reln, blkno, true);
+	buffer = XLogReadBuffer(rnode, blkno, true);
 	Assert(BufferIsValid(buffer));
 	page = (Page) BufferGetPage(buffer);
 
@@ -501,8 +500,7 @@ The standard replay-routine pattern for this case is
 	if (record->xl_info & XLR_BKP_BLOCK_n)
 		<< do nothing, page was rewritten from logged copy >>;
 
-	reln = XLogOpenRelation(rnode);
-	buffer = XLogReadBuffer(reln, blkno, false);
+	buffer = XLogReadBuffer(rnode, blkno, false);
 	if (!BufferIsValid(buffer))
 		<< do nothing, page has been deleted >>;
 	page = (Page) BufferGetPage(buffer);

src/backend/catalog/storage.c

@@ -505,7 +505,7 @@ smgr_redo(XLogRecPtr lsn, XLogRecord *record)
 		/*
 		 * Forcibly create relation if it doesn't exist (which suggests that
 		 * it was dropped somewhere later in the WAL sequence).  As in
-		 * XLogOpenRelation, we prefer to recreate the rel and replay the log
+		 * XLogReadBuffer, we prefer to recreate the rel and replay the log
 		 * as best we can until the drop is seen.
 		 */
 		smgrcreate(reln, MAIN_FORKNUM, true);