cgroup: remove stray references to css_id

Trivial: remove the few stray references to css_id, which itself
was removed in v3.13's 2ff2a7d03bbe "cgroup: kill css_id".

Signed-off-by: Hugh Dickins <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

drivers/md/bcache/request.c

···
 static void bcachecg_destroy(struct cgroup *cgroup)
 {
 	struct bch_cgroup *cg = cgroup_to_bcache(cgroup);
-	free_css_id(&bcache_subsys, &cg->css);
 	kfree(cg);
 }
 

include/linux/cgroup.h

···
 struct cgroup_subsys;
 struct inode;
 struct cgroup;
-struct css_id;
 
 extern int cgroup_init_early(void);
 extern int cgroup_init(void);
···
 	struct cgroup_subsys_state *parent;
 
 	unsigned long flags;
-	/* ID for this css, if possible */
-	struct css_id __rcu *id;
 
 	/* percpu_ref killing and RCU release */
 	struct rcu_head rcu_head;

mm/page_cgroup.c

···
  * lookup_swap_cgroup_id - lookup mem_cgroup id tied to swap entry
  * @ent: swap entry to be looked up.
  *
- * Returns CSS ID of mem_cgroup at success. 0 at failure. (0 is invalid ID)
+ * Returns ID of mem_cgroup at success. 0 at failure. (0 is invalid ID)
  */
 unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
 {