cgroup: don't use idr_remove_all()

idr_destroy() can destroy idr by itself and idr_remove_all() is being
deprecated.  Drop its usage.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/cgroup.c

@@ -4618,10 +4618,8 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
 	offline_css(ss, dummytop);
 	ss->active = 0;
 
-	if (ss->use_id) {
-		idr_remove_all(&ss->idr);
+	if (ss->use_id)
 		idr_destroy(&ss->idr);
-	}
 
 	/* deassign the subsys_id */
 	subsys[ss->subsys_id] = NULL;