cgroup: remove unused CGRP_SANE_BEHAVIOR

This cgroup flag has never been used.  Only CGRP_ROOT_SANE_BEHAVIOR is
used.  Remove it.
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/cgroup.h

@@ -140,8 +140,6 @@ enum {
 	 * specified at mount time and thus is implemented here.
 	 */
 	CGRP_CPUSET_CLONE_CHILDREN,
-	/* see the comment above CGRP_ROOT_SANE_BEHAVIOR for details */
-	CGRP_SANE_BEHAVIOR,
 };
 
 struct cgroup {