xfs: remove XFS_TRANS_DEBUG dead code

Remove the leftover XFS_TRANS_DEBUG dead code following the previous
cleaning up of it in commits ec47eb6b.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>