vhost-test: drop flush after vhost_dev_cleanup

vhost-test: drop flush after vhost_dev_cleanup

The flush after vhost_dev_cleanup is not needed because:

1. It doesn't do anything. vhost_dev_cleanup will stop the worker thread
so the flush call will just return since the worker has not device.

2. It's not needed. The comment about jobs re-queueing themselves does
not look correct because handle_vq does not requeue work.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220517180850.198915-8-michael.christie@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>