btrfs: remove pointless writepages callback wrapper

There's no point in having a static writepages callback in inode.c that
does nothing besides calling extent_writepages from extent_io.c.
So just remove the callback at inode.c and rename extent_writepages()
to btrfs_writepages().
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -2246,8 +2246,7 @@ void extent_write_locked_range(struct inode *inode, struct page *locked_page,
 	submit_write_bio(&bio_ctrl, found_error ? ret : 0);
 }
 
-int extent_writepages(struct address_space *mapping,
-		      struct writeback_control *wbc)
+int btrfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
 {
 	struct inode *inode = mapping->host;
 	int ret = 0;

fs/btrfs/extent_io.h

@@ -237,8 +237,7 @@ int btrfs_read_folio(struct file *file, struct folio *folio);
 void extent_write_locked_range(struct inode *inode, struct page *locked_page,
 			       u64 start, u64 end, struct writeback_control *wbc,
 			       bool pages_dirty);
-int extent_writepages(struct address_space *mapping,
-		      struct writeback_control *wbc);
+int btrfs_writepages(struct address_space *mapping, struct writeback_control *wbc);
 int btree_write_cache_pages(struct address_space *mapping,
 			    struct writeback_control *wbc);
 void btrfs_readahead(struct readahead_control *rac);

fs/btrfs/inode.c

@@ -7923,12 +7923,6 @@ static int btrfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 	return ret;
 }
 
-static int btrfs_writepages(struct address_space *mapping,
-			    struct writeback_control *wbc)
-{
-	return extent_writepages(mapping, wbc);
-}
-
 /*
  * For release_folio() and invalidate_folio() we have a race window where
  * folio_end_writeback() is called but the subpage spinlock is not yet released.