Remove old isolate API and update all code in the repository to use

tests/isolate/v2_spawn_function_custom_class_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.
-
-// Create a user-defined class in a new isolate.
-//
-// Regression test for vm bug 2235: We were forgetting to finalize
-// classes in new isolates started using the v2 api.
-
-#library('spawn_tests');
-#import('dart:isolate');
-#import('../../lib/unittest/unittest.dart');
-
-class MyClass {
-  var myVar = 'there';
-  myFunc(msg) {
-    return '$msg $myVar';
-  }
-}
-
-child() {
-  port.receive((msg, reply) {
-      reply.send('re: ${new MyClass().myFunc(msg)}');
-    });
-}
-
-main() {
-  test('message - reply chain', () {
-    ReceivePort port = new ReceivePort();
-    port.receive(expectAsync(msg, _) {
-      port.close();
-      expect(msg, equals('re: hi there'));
-    });
-
-    SendPort s = spawnFunction(child);
-    s.send('hi', port.toSendPort());
-  });
-}