The empty cgroup notification mechanism currently implemented in
cgroup is tragically outdated.  Forking and execing userland process
stopped being a viable notification mechanism more than a decade ago.
We're gonna have a saner mechanism.  Let's make it clear that this
abomination is going away.

Mark "notify_on_release" and "release_agent" with CFTYPE_INSANE.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NLi Zefan <lizefan@huawei.com>