Make "--no-packages-dir" the default.

test/get/hosted/does_no_network_requests_when_possible_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.
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
@@ skipping 12 matching lines @@
     pubGet();
 
     // Clear the cache. We don't care about anything that was served during
     // the initial get.
     globalServer.clearRequestedPaths();
 
     // Run the solver again now that it's cached.
     pubGet();
 
     d.cacheDir({"foo": "1.2.0"}).validate();
-    d.packagesDir({"foo": "1.2.0"}).validate();
+    d.appPackagesFile({"foo": "1.2.0"}).validate();
 
     // The get should not have done any network requests since the lock file is
     // up to date.
     globalServer.requestedPaths.then((paths) {
       expect(paths, isEmpty);
     });
   });
 }