bcache: remove useless bucket_pages()

It seems alloc_bucket_pages() is the only user of bucket_pages().
Considering alloc_bucket_pages() is removed from bcache code, it is safe
to remove the useless macro bucket_pages() now.
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/bcache.h

@@ -757,7 +757,6 @@ struct bbio {
 #define btree_default_blocks(c)						\
 	((unsigned int) ((PAGE_SECTORS * (c)->btree_pages) >> (c)->block_bits))
 
-#define bucket_pages(c)		((c)->sb.bucket_size / PAGE_SECTORS)
 #define bucket_bytes(c)		((c)->sb.bucket_size << 9)
 #define block_bytes(ca)		((ca)->sb.block_size << 9)