cifs: 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.  Now that cifs implements ->migrate_folio and
doesn't call generic_writepages, the writepage method can be removed.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/file.c

@@ -2868,13 +2868,6 @@ cifs_writepage_locked(struct page *page, struct writeback_control *wbc)
 	return rc;
 }
 
-static int cifs_writepage(struct page *page, struct writeback_control *wbc)
-{
-	int rc = cifs_writepage_locked(page, wbc);
-	unlock_page(page);
-	return rc;
-}
-
 static int cifs_write_end(struct file *file, struct address_space *mapping,
 			loff_t pos, unsigned len, unsigned copied,
 			struct page *page, void *fsdata)
@@ -5247,7 +5240,6 @@ static bool cifs_dirty_folio(struct address_space *mapping, struct folio *folio)
 const struct address_space_operations cifs_addr_ops = {
 	.read_folio = cifs_read_folio,
 	.readahead = cifs_readahead,
-	.writepage = cifs_writepage,
 	.writepages = cifs_writepages,
 	.write_begin = cifs_write_begin,
 	.write_end = cifs_write_end,
@@ -5272,7 +5264,6 @@ const struct address_space_operations cifs_addr_ops = {
  */
 const struct address_space_operations cifs_addr_ops_smallbuf = {
 	.read_folio = cifs_read_folio,
-	.writepage = cifs_writepage,
 	.writepages = cifs_writepages,
 	.write_begin = cifs_write_begin,
 	.write_end = cifs_write_end,