The patch (7235acdb) changed the way of the work
flushing in which the queued seq, done seq, and the
flushing are not used anymore. Then remove them now.

Fixes: 7235acdb ("vhost: simplify work flushing")
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>