Revert "Zone support for Futures."

tests/lib/async/run_zoned6_test.dart

-// Copyright (c) 2013, 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.
-
-import "package:expect/expect.dart";
-import 'dart:async';
-import 'dart:isolate';
-
-main() {
-  // We keep a ReceivePort open until all tests are done. This way the VM will
-  // hang if the callbacks are not invoked and the test will time out.
-  var port = new ReceivePort();
-  // Ensure that `runZoned`'s onError handles synchronous errors but delegates
-  // to the top-level when the handler returns false.
-  try {
-    runZonedExperimental(() { throw 0; },
-                        onError: (e) {
-                          Expect.equals(0, e);
-                          port.close();
-                          throw e;  /// 01: runtime error
-                        });
-  } catch (e) {
-    // We should never see an error here.
-    if (true)  /// 01: continued
-      rethrow;
-  }
-}