zap_other_threads: don't optimize thread_group_empty() case

Nowadays thread_group_empty() and next_thread() are simple list operations,
this optimization doesn't make sense: we are doing exactly same check one
line below.
Signed-off-by: NOleg Nesterov <oleg@tv-sign.ru>
Acked-by: NRoland McGrath <roland@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

@@ -985,9 +985,6 @@ void zap_other_threads(struct task_struct *p)
 	p->signal->flags = SIGNAL_GROUP_EXIT;
 	p->signal->group_stop_count = 0;
 
-	if (thread_group_empty(p))
-		return;
-
 	for (t = next_thread(p); t != p; t = next_thread(t)) {
 		/*
 		 * Don't bother with already dead threads