scsi: core: Remove <scsi/scsi_request.h>

This header is empty now except for an include of <linux/blk-mq.h>, so
remove it.

Link: https://lore.kernel.org/r/20220224175552.988286-9-hch@lst.de


Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>