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

tests/isolate/v2_spawn_uri_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 URI
-// Note: the following comment is used by test.dart to additionally compile the
-// other isolate's code.
-// OtherScripts=v2_spawn_uri_child_isolate.dart
-#library('spawn_tests');
-#import('../../lib/unittest/unittest.dart');
-#import('dart:isolate');
-
-main() {
-  test('isolate fromUri - send and reply', () {
-    ReceivePort port = new ReceivePort();
-    port.receive(expectAsync2((msg, _) {
-      expect(msg, equals('re: hi'));
-      port.close();
-    }));
-
-    // TODO(eub): make this work for non-JS targets.
-    SendPort s = spawnUri('v2_spawn_uri_child_isolate.js');
-    s.send('hi', port.toSendPort());
-  });
-}