blk-mq: delete dead struct blk_mq_hw_ctx->queued field

This counter is not used anywhere, so delete it.
Signed-off-by: NChengming Zhou <zhouchengming@bytedance.com>
Reviewed-by: NBart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230720095512.1403123-1-chengming.zhou@linux.devSigned-off-by: NJens Axboe <axboe@kernel.dk>

include/linux/blk-mq.h

@@ -397,8 +397,6 @@ struct blk_mq_hw_ctx {
 	 */
 	struct blk_mq_tags	*sched_tags;
 
-	/** @queued: Number of queued requests. */
-	unsigned long		queued;
 	/** @run: Number of dispatched requests. */
 	unsigned long		run;