omfs: remove ->writepage

->writepage is a very inefficient method to write back data, and only
used through write_cache_pages or a a fallback when no ->migrate_folio
method is present.

Set ->migrate_folio to the generic buffer_head based helper, and remove
the ->writepage implementation.

Link: https://lkml.kernel.org/r/20221202102644.770505-8-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Bob Copeland <me@bobcopeland.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/omfs/file.c

@@ -294,11 +294,6 @@ static void omfs_readahead(struct readahead_control *rac)
 	mpage_readahead(rac, omfs_get_block);
 }
 
-static int omfs_writepage(struct page *page, struct writeback_control *wbc)
-{
-	return block_write_full_page(page, omfs_get_block, wbc);
-}
-
 static int
 omfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
 {
@@ -375,10 +370,10 @@ const struct address_space_operations omfs_aops = {
 	.invalidate_folio = block_invalidate_folio,
 	.read_folio = omfs_read_folio,
 	.readahead = omfs_readahead,
-	.writepage = omfs_writepage,
 	.writepages = omfs_writepages,
 	.write_begin = omfs_write_begin,
 	.write_end = generic_write_end,
 	.bmap = omfs_bmap,
+	.migrate_folio = buffer_migrate_folio,
 };