virtio-iommu: Revert transient enablement of IOMMU MR in bypass mode

virtio-iommu: Revert transient enablement of IOMMU MR in bypass mode

In 94df5b2180d6 ("virtio-iommu: Fix 64kB host page size VFIO device
assignment"), in case of bypass mode, we transiently enabled the
IOMMU MR to allow the set_page_size_mask() to be called and pass
information about the page size mask constraint of cold plugged
VFIO devices. Now we do not use the IOMMU MR callback anymore, we
can just get rid of this hack.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>