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

tests/isolate/v2_spawn_function_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.
-
-// Example of spawning an isolate from a function.
-#library('spawn_tests');
-#import('dart:isolate');
-#import('../../lib/unittest/unittest.dart');
-
-child() {
-  port.receive((msg, reply) => reply.send('re: $msg'));
-}
-
-main() {
-  test('message - reply chain', () {
-    ReceivePort port = new ReceivePort();
-    port.receive(expectAsync(msg, _) {
-      port.close();
-      expect(msg, equals('re: hi'));
-    });
-
-    SendPort s = spawnFunction(child);
-    s.send('hi', port.toSendPort());
-  });
-}