scsi: remove the SCSI OSD library

Now that all the users are gone the SCSI OSD library can be removed as
well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>