Now that the broken power state control is gone, it appears to serve
no purpose.  Just delete it.  NVME devices don't have a concept of
started vs stopped anyway.
Signed-off-by: NAndy Lutomirski <luto@kernel.org>
Reviewed-by: NKeith Busch <keith.busch@intel.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>