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

test/get/hosted/avoid_network_requests_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 20 matching lines @@
 
     // Add "bar" to the dependencies.
     d.appDir({
       "foo": "any",
       "bar": "any"
     }).create();
 
     // Run the solver again.
     pubGet();
 
-    d.packagesDir({
+    d.appPackagesFile({
       "foo": "1.2.0",
       "bar": "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, unorderedEquals([
         // Bar should be requested because it's new, but not foo.
         "api/packages/bar",
         // Need to download it.
         "packages/bar/versions/1.2.0.tar.gz"
       ]));
     });
   });
 }