ide: remove REQ_TYPE_ATA_CMD

Based on the earlier work by Tejun Heo.

All users are gone so we can finally remove it.

Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

include/linux/blkdev.h

@@ -143,7 +143,6 @@ enum rq_cmd_type_bits {
 	 * use REQ_TYPE_SPECIAL and use rq->cmd[0] with the range of driver
 	 * private REQ_LB opcodes to differentiate what type of request this is
 	 */
-	REQ_TYPE_ATA_CMD,
 	REQ_TYPE_ATA_TASKFILE,
 	REQ_TYPE_ATA_PC,
 };