cgroup: remove CGRP_ROOT_OPTION_MASK

cgroup_root->flags only contains CGRP_ROOT_* flags and there's no
reason to mask the flags.  Remove CGRP_ROOT_OPTION_MASK.

This doesn't cause any behavior differences.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

include/linux/cgroup.h

@@ -320,9 +320,6 @@ enum {
 
 	CGRP_ROOT_NOPREFIX	= (1 << 1), /* mounted subsystems have no named prefix */
 	CGRP_ROOT_XATTR		= (1 << 2), /* supports extended attributes */
-
-	/* mount options live below bit 16 */
-	CGRP_ROOT_OPTION_MASK	= (1 << 16) - 1,
 };
 
 /*