Btrfs: fix the error handling wrt orphan items

There are several places where we BUG_ON() if we fail to remove the orphan items
and such, which is not ok, so remove those and either abort or just carry on.
This also fixes a problem where if we couldn't start a transaction we wouldn't
actually remove the orphan item reserve for the inode.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>