bcache: Remove dead references to cache_readaheads

The cache_readaheads stat counter is not used anymore and should be
removed.

Signed-off-by: Andrea Tomassetti <andrea.tomassetti-opensource@devo.com>
Signed-off-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/r/20230615121223.22502-4-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Andrea Tomassetti

Documentation/admin-guide/bcache.rst

@@ -508,9 +508,6 @@ cache_miss_collisions
   cache miss, but raced with a write and data was already present (usually 0
   since the synchronization for cache misses was rewritten)
 
-cache_readaheads
-  Count of times readahead occurred.
-
 Sysfs - cache set
 ~~~~~~~~~~~~~~~~~
 

drivers/md/bcache/stats.h

@@ -18,7 +18,6 @@ struct cache_stats {
 	unsigned long cache_misses;
 	unsigned long cache_bypass_hits;
 	unsigned long cache_bypass_misses;
-	unsigned long cache_readaheads;
 	unsigned long cache_miss_collisions;
 	unsigned long sectors_bypassed;