blk-throttle: remove more latency dead-code

The struct 'latency_bucket' and the #define 'request_bucket_index'
are unused since
commit bf20ab5 ("blk-throttle: remove CONFIG_BLK_DEV_THROTTLING_LOW")

and the 'LATENCY_BUCKET_SIZE' #define was only used by the
'request_bucket_index' define.

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://lore.kernel.org/r/20240727155824.1000042-1-linux@treblig.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Dr. David Alan Gilbert

block/blk-throttle.c

@@ -31,14 +31,6 @@ static struct workqueue_struct *kthrotld_workqueue;
 
 #define rb_entry_tg(node)	rb_entry((node), struct throtl_grp, rb_node)
 
-/* We measure latency for request size from <= 4k to >= 1M */
-#define LATENCY_BUCKET_SIZE 9
-
-struct latency_bucket {
-	unsigned long total_latency; /* ns / 1024 */
-	int samples;
-};
-
 struct throtl_data
 {
 	/* service tree for active throtl groups */
@@ -116,9 +108,6 @@ static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
 	return tg->iops[rw];
 }
 
-#define request_bucket_index(sectors) \
-	clamp_t(int, order_base_2(sectors) - 3, 0, LATENCY_BUCKET_SIZE - 1)
-
 /**
  * throtl_log - log debug message via blktrace
  * @sq: the service_queue being reported