scsi: Cleanup not used anymore SCSIBusInfo{hotplug, hot_unplug} fields

SCSI subsytem was converted to hotplug handler API and
doesn't use SCSIBusInfo{hotplug, hot_unplug} fields and
related callbacks anymore.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>