nvme: kick requeue list when requeueing a request instead of when starting the queues

When we requeue a request, we can always insert the request
back to the scheduler instead of doing it when restarting
the queues and kicking the requeue work, so get rid of
the requeue kick in nvme (core and drivers).

Also, now there is no need start hw queues in nvme_kill_queues
We don't stop the hw queues anymore, so no need to
start them.

Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>