btrfs: extent_io: Kill dead condition in extent_write_cache_pages()

Since __extent_writepage() will no longer return >0 value,
(ret == AOP_WRITEPAGE_ACTIVATE) will never be true.

Kill that dead branch.
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -3974,11 +3974,6 @@ static int extent_write_cache_pages(struct address_space *mapping,
 			}
 
 			ret = __extent_writepage(page, wbc, epd);
-
-			if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
-				unlock_page(page);
-				ret = 0;
-			}
 			if (ret < 0) {
 				/*
 				 * done_index is set past this page,