Commits
David Sterba committed 58409edd2d5
btrfs: kill unused writepage_io_hook callback
It seems to be long time unused, since 2008 and
6885f308b5570 ("Btrfs: Misc 2.6.25 updates").
Propagating the removal touches some code but has no functional effect.
Signed-off-by: David Sterba <dsterba@suse.com>