exec: consolidate 2 fast-paths

Now that we don't pre-allocate the new ->sighand, we can kill the first fast
path, it doesn't make sense any longer. At best, it can save one "list_empty()"
check but leads to the code duplication.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -752,15 +752,6 @@ static int de_thread(struct task_struct *tsk)
 	struct task_struct *leader = NULL;
 	int count;
 
-	/*
-	 * If we don't share sighandlers, then we aren't sharing anything
-	 * and we can just re-use it all.
-	 */
-	if (atomic_read(&oldsighand->count) <= 1) {
-		exit_itimers(sig);
-		return 0;
-	}
-
 	if (thread_group_empty(tsk))
 		goto no_thread_group;