idle: Remove stale RCU comment

The call of rcu_idle_enter() from within cpuidle_idle_call() was
removed in commit 1098582a ("sched,idle,rcu: Push rcu_idle deeper
into the idle path") which makes the comment out of place.
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/5b936388-47df-4050-9229-6617a6c2bba5@arm.com

kernel/sched/idle.c

@@ -179,12 +179,6 @@ static void cpuidle_idle_call(void)
 		return;
 	}
 
-	/*
-	 * The RCU framework needs to be told that we are entering an idle
-	 * section, so no more RCU read side critical sections and one more
-	 * step to the grace period
-	 */
-
 	if (cpuidle_not_available(drv, dev)) {
 		tick_nohz_idle_stop_tick();