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

tests/isolate/v2_compute_this_script_browser_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.
-
-// Test that spawn works even when there are many script files in the page.
-// This requires computing correctly the URL to the orignal script, so we can
-// pass it to the web worker APIs.
-#library('compute_this_script');
-
-#import('dart:html');
-#import('dart:isolate');
-
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
-
-child() {
-  port.receive((msg, reply) {
-    reply.send('re: $msg');
-    port.close();
-  });
-}
-
-main() {
-  useHtmlConfiguration();
-  var script = document.$dom_createElement('script');
-  document.body.$dom_appendChild(script);
-  test('spawn with other script tags in page', () {
-    ReceivePort port = new ReceivePort();
-    port.receive(expectAsync2((msg, _) {
-      expect(msg, equals('re: hi'));
-      port.close();
-    }));
-
-    SendPort s = spawnFunction(child);
-    s.send('hi', port.toSendPort());
-  });
-}