Revert "Signal handling."

tests/standalone/io/signals_test_script.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import "dart:io";
-
-void main(args) {
-  int usr1Count = int.parse(args[0]);
-  int usr2Count = int.parse(args[1]);
-  var sub1;
-  var sub2;
-  void check() {
-    if (usr1Count < 0 || usr2Count < 0) exit(1);
-    if (usr1Count == 0 && usr2Count == 0) {
-      sub1.cancel();
-      sub2.cancel();
-    }
-    print("ready");
-  }
-  sub1 = ProcessSignal.SIGUSR1.watch().listen((signal) {
-    if (signal != ProcessSignal.SIGUSR1) exit(1);
-    usr1Count--;
-    check();
-  });
-  sub2 = ProcessSignal.SIGUSR2.watch().listen((signal) {
-    if (signal != ProcessSignal.SIGUSR2) exit(1);
-    usr2Count--;
-    check();
-  });
-  check();
-}