Clean up isolate tests.

tests/isolate/spawn_function_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.
-
-// Negative test to make sure that we are reaching all assertions.
-library spawn_tests;
-import 'dart:isolate';
-import '../../pkg/unittest/lib/unittest.dart';
-
-child(args) {
-  var msg = args[0];
-  var reply = args[1];
-  reply.send('re: $msg');
-}
-
-main() {
-  test('message - reply chain', () {
-    ReceivePort port = new ReceivePort();
-    Isolate.spawn(child, ['hi', port.sendPort]);
-    port.listen(expectAsync1((msg) {
-      port.close();
-      expect(msg, equals('re: hello')); // should be hi, not hello
-    }));
-  });
-}