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

test/sdk_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS d.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 d.file.
 
 import 'package:path/path.dart' as p;
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import 'package:pub/src/exit_codes.dart' as exit_codes;
 
@@ skipping 22 matching lines @@
       pubCommand(command,
           environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')});
 
       d.dir(appPath, [
         d.packagesFile({
           'myapp': '.',
           'foo': p.join(sandboxDir, 'flutter', 'packages', 'foo'),
           'bar': '1.0.0'
         })
       ]).validate();
-
-      d.packagesDir({'foo': '0.0.1', 'bar': '1.0.0'}).validate();
     });
 
     group("fails if", () {
       integration("the version constraint doesn't match", () {
         d.appDir({"foo": {"sdk": "flutter", "version": "^1.0.0"}}).create();
         pubCommand(command,
             environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')},
             error: 'Package foo has no versions that match >=1.0.0 <2.0.0 '
                      'derived from:\n'
                    '- myapp depends on version ^1.0.0');
       });
 
       integration("the SDK is unknown", () {
         d.appDir({"foo": {"sdk": "unknown"}}).create();
         pubCommand(command,
             error: 'Unknown SDK "unknown".\n'
                    'Depended on by:\n'
                    '- myapp',
             exitCode: exit_codes.UNAVAILABLE);
       });
 
       integration("the SDK is unavailable", () {
         d.appDir({"foo": {"sdk": "flutter"}}).create();
         pubCommand(command,
             error: 'The Flutter SDK is not available.\n'
                    'Depended on by:\n'
                    '- myapp',
             exitCode: exit_codes.UNAVAILABLE);
       });
- 
+
       integration("the SDK doesn't contain the package", () {
         d.appDir({"bar": {"sdk": "flutter"}}).create();
         pubCommand(command,
             environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')},
             error: 'Could not find package bar in the Flutter SDK.\n'
                    'Depended on by:\n'
                    '- myapp',
             exitCode: exit_codes.UNAVAILABLE);
       });
 
       integration("the Dart SDK doesn't contain the package", () {
         d.appDir({"bar": {"sdk": "dart"}}).create();
         pubCommand(command,
             error: 'Could not find package bar in the Dart SDK.\n'
                    'Depended on by:\n'
                    '- myapp',
             exitCode: exit_codes.UNAVAILABLE);
       });
     });
   });
 }