Btrfs: delete dead code in btrfs_orphan_add()

btrfs_orphan_add() has had this case commented out since it was first
introduced in commit d68fc57b

 ("Btrfs: Metadata reservation for
orphan inodes"). Most of the orphan cleanup code has been rewritten
since then, so it's safe to say that this code isn't needed.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
[ switch to bool ]
Signed-off-by: David Sterba <dsterba@suse.com>