nvme: Remove SCSI translations

The SCSI-to-NVMe translations were added to assist storage applications
utilizing SG_IO transitioning to NVMe. It was always recommended,
however, to use native NVMe for device management as too much is lost
in translation and the maintenance burden in keeping this kludgey
layer around has been neglected such that much of the translations are
completely broken.

This patch removes SG_IO handling from NVMe to avoid any confusion
regarding maintenance support for this interface. The config option for
NVMe SCSI emulation has been disabled by default since 4.5. The driver
has supported native nvme user commands since the beginning, and native
tooling is publicly available for use or as reference for anyone writing
their own tools, so there's no excuse for hanging onto a broken crutch.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Guan Junxiong <guanjunxiong@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>