bcache: remove useless alloc_bucket_pages()

Now no one uses alloc_bucket_pages() anymore, remove it from bcache.h.
Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/super.c

@@ -1831,9 +1831,6 @@ void bch_cache_set_unregister(struct cache_set *c)
 	bch_cache_set_stop(c);
 }
 
-#define alloc_bucket_pages(gfp, c)			\
-	((void *) __get_free_pages(__GFP_ZERO|__GFP_COMP|gfp, ilog2(bucket_pages(c))))
-
 #define alloc_meta_bucket_pages(gfp, sb)		\
 	((void *) __get_free_pages(__GFP_ZERO|__GFP_COMP|gfp, ilog2(meta_bucket_pages(sb))))