sched/headers, cgroups: Remove the threadgroup_change_*() wrappery

threadgroup_change_begin()/end() is a pointless wrapper around
cgroup_threadgroup_change_begin()/end(), minus a might_sleep()
in the !CONFIG_CGROUPS=y case.

Remove the wrappery, move the might_sleep() (the down_read()
already has a might_sleep() check).

This debloats <linux/sched.h> a bit and simplifies this API.

Update all call sites.

No change in functionality.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/signal.c b/kernel/signal.c
index 214a8fe..bae3585 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2395,11 +2395,11 @@
 	 * @tsk is about to have PF_EXITING set - lock out users which
 	 * expect stable threadgroup.
 	 */
-	threadgroup_change_begin(tsk);
+	cgroup_threadgroup_change_begin(tsk);
 
 	if (thread_group_empty(tsk) || signal_group_exit(tsk->signal)) {
 		tsk->flags |= PF_EXITING;
-		threadgroup_change_end(tsk);
+		cgroup_threadgroup_change_end(tsk);
 		return;
 	}
 
@@ -2410,7 +2410,7 @@
 	 */
 	tsk->flags |= PF_EXITING;
 
-	threadgroup_change_end(tsk);
+	cgroup_threadgroup_change_end(tsk);
 
 	if (!signal_pending(tsk))
 		goto out;