scsi: Drop SCSIReqOps.cancel_io The only two implementations are identical to each other, with nothing specific to device: they only call bdrv_aio_cancel with the SCSIRequest.aiocb. Let's move it to scsi-bus. Signed-off-by: Fam Zheng <famz@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>