nvme/scsi: Remove power management support

As far as I can tell, there is basically nothing correct about this
code.  It misinterprets npss (off-by-one).  It hardcodes a bunch of
power states, which is nonsense, because they're all just indices
into a table that software needs to parse.  It completely ignores
the distinction between operational and non-operational states.
And, until 4.8, if all of the above magically succeeded, it would
dereference a NULL pointer and OOPS.

Since this code appears to be useless, just delete it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jay Freyensee <james_p_freyensee@linux.intel.com>
Tested-by: Jay Freyensee <james_p_freyensee@linux.intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>