block: remove some blk_mq_hw_ctx debugfs entries

Just like the blk_mq_ctx counterparts, we've got a bunch of counters
in here that are only for debugfs and are of questionnable value. They
are:

- dispatched, index of how many requests were dispatched in one go

- poll_{considered,invoked,success}, which track poll sucess rates. We're
  confident in the iopoll implementation at this point, don't bother
  tracking these.

As a bonus, this shrinks each hardware queue from 576 bytes to 512 bytes,
dropping a whole cacheline.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blk-mq.h

@@ -341,9 +341,6 @@ struct blk_mq_hw_ctx {
 	unsigned long		queued;
 	/** @run: Number of dispatched requests. */
 	unsigned long		run;
-#define BLK_MQ_MAX_DISPATCH_ORDER	7
-	/** @dispatched: Number of dispatch requests by queue. */
-	unsigned long		dispatched[BLK_MQ_MAX_DISPATCH_ORDER];
 
 	/** @numa_node: NUMA node the storage adapter has been connected to. */
 	unsigned int		numa_node;
@@ -363,13 +360,6 @@ struct blk_mq_hw_ctx {
 	/** @kobj: Kernel object for sysfs. */
 	struct kobject		kobj;
 
-	/** @poll_considered: Count times blk_mq_poll() was called. */
-	unsigned long		poll_considered;
-	/** @poll_invoked: Count how many requests blk_mq_poll() polled. */
-	unsigned long		poll_invoked;
-	/** @poll_success: Count how many polled requests were completed. */
-	unsigned long		poll_success;
-
 #ifdef CONFIG_BLK_DEBUG_FS
 	/**
 	 * @debugfs_dir: debugfs directory for this hardware queue. Named