Move timer tests to async tests.

tests/isolate/timer_cancel1_test.dart

-// Copyright (c) 2012, 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.
-
-library timer_cancel1_test;
-import 'dart:async';
-import '../../pkg/unittest/lib/unittest.dart';
-
-main() {
-  // Test that a timeout handler can cancel another.
-  test("timer cancel1 test", () {
-    var canceleeTimer;
-    var cancelerTimer;
-
-    void unreachable() {
-      fail("A canceled timeout handler should be unreachable.");
-    }
-
-    void handler() {
-      canceleeTimer.cancel();
-    }
-
-    cancelerTimer = new Timer(const Duration(milliseconds: 1),
-                              expectAsync0(handler));
-    canceleeTimer = new Timer(const Duration(milliseconds: 1000),
-                              expectAsync0(unreachable, count: 0));
-  });
-}