vfio: revert "iommu driver notify callback"

Revert this dead code:
  commit ec5e3294 ("vfio: iommu driver notify callback")

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/1675184289-267876-8-git-send-email-steven.sistare@oracle.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>