cgroup: Remove stale comments

- The default root is where we can create v2 cgroups.
- The __DEVEL__sane_behavior mount option has been removed long long ago.
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cgroup.c

@@ -153,11 +153,7 @@ static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
 
 static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);
 
-/*
- * The default hierarchy, reserved for the subsystems that are otherwise
- * unattached - it never has more than a single cgroup, and all tasks are
- * part of that cgroup.
- */
+/* the default hierarchy */
 struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
 
@@ -251,9 +247,6 @@ bool cgroup_ssid_enabled(int ssid)
  * cases where a subsystem should behave differnetly depending on the
  * interface version.
  *
- * The set of behaviors which change on the default hierarchy are still
- * being determined and the mount option is prefixed with __DEVEL__.
- *
  * List of changed behaviors:
  *
  * - Mount options "noprefix", "xattr", "clone_children", "release_agent"