Documentation/feature-removal-schedule.txt: remove ns_cgroup from feature-removal-schedule.txt

Commit a77aea9201 ("cgroup: remove the ns_cgroup") removed the
ns_cgroup but it forgot to remove the related doc in
feature-removal-schedule.txt.

Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Daniel Lezcano <daniel.lezcano@free.fr>
Cc: Serge E.  Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/feature-removal-schedule.txt

@@ -481,23 +481,6 @@ Who:	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
 
 ----------------------------
 
-What:   namespace cgroup (ns_cgroup)
-When:   2.6.38
-Why:    The ns_cgroup leads to some problems:
-	* cgroup creation is out-of-control
-	* cgroup name can conflict when pids are looping
-	* it is not possible to have a single process handling
-	a lot of namespaces without falling in a exponential creation time
-	* we may want to create a namespace without creating a cgroup
-
-	The ns_cgroup is replaced by a compatibility flag 'clone_children',
-	where a newly created cgroup will copy the parent cgroup values.
-	The userspace has to manually create a cgroup and add a task to
-	the 'tasks' file.
-Who:    Daniel Lezcano <daniel.lezcano@free.fr>
-
-----------------------------
-
 What:	iwlwifi disable_hw_scan module parameters
 When:	2.6.40
 Why:	Hareware scan is the prefer method for iwlwifi devices for