[XFS] remove xfs_vfsops.h

The only thing left is xfs_do_force_shutdown which already has a defintion
in xfs_mount.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Niv Sardi <xaiki@sgi.com>