Clean up isolate tests.

tests/isolate/isolate_negative_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.
-
-// Dart test program for testing that isolates are spawned.
-
-library IsolateNegativeTest;
-import "package:expect/expect.dart";
-import 'dart:isolate';
-import '../../pkg/unittest/lib/unittest.dart';
-
-void entry(SendPort replyTo) {
-  replyTo.send("foo");
-}
-
-main() {
-  test("ensure isolate code is executed", () {
-    ReceivePort response = new ReceivePort();
-    Isolate.spawn(entry, response.sendPort);
-    response.first.then(expectAsync1((message) {
-      expect("Expected fail", isTrue);   // <=-------- Should fail here.
-    }));
-  });
-}