xfs: remove the debug-only q_transp field from struct xfs_dquot

The field is only used for a few assertations.  Shrink the dqout
structure instead, similarly to what commit f3ca8738
("xfs: remove i_transp") did for the xfs_inode.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>