NVMe: within nvme_free_queues(), delete RCU sychro/deferred free

Converting from to blk-queue got rid of the driver's RCU
locking-on-queue, so removing unnecessary RCU locking-on-queue
artefacts.

Reviewed-by: Keith Busch <keith.busch@intel.com>

Signed-off-by: Kelly Nicole Kaoudis <kaoudis@colorado.edu>
Signed-off-by: Jens Axboe <axboe@fb.com>