null_blk: remove unused fields in 'nullb_cmd'

'list', 'll_list' and 'csd' are no longer used.

The 'list' is not used since it was introduced by commit f2298c0
("null_blk: multi queue aware block test driver").

The 'll_list' is no longer used since commit 3c395a9 ("null_blk: set a
separate timer for each command").

The 'csd' is no longer used since commit ce2c350 ("null_blk: use
blk_complete_request and blk_mq_complete_request").

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk.h

@@ -14,9 +14,6 @@
 #include <linux/fault-inject.h>
 
 struct nullb_cmd {
-	struct list_head list;
-	struct llist_node ll_list;
-	struct __call_single_data csd;
 	struct request *rq;
 	struct bio *bio;
 	unsigned int tag;

drivers/block/null_blk_main.c

@@ -1518,8 +1518,6 @@ static int setup_commands(struct nullb_queue *nq)
 
 	for (i = 0; i < nq->queue_depth; i++) {
 		cmd = &nq->cmds[i];
-		INIT_LIST_HEAD(&cmd->list);
-		cmd->ll_list.next = NULL;
 		cmd->tag = -1U;
 	}