This reverts commit df91055d.

This is because:
- vhost support virtio 1.0 now
- transport code (e.g virtio-pci) set this feature when modern is
  enabled, setting this unconditionally will break disable-modern=on.

Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>