Get rid of all the library tags.

test/build/allows_arbitrary_modes_test.dart

 // Copyright (c) 2013, 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 file.
 
-library pub_tests;
-
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 const TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 class ModeTransformer extends Transformer {
   final BarbackSettings settings;
@@ skipping 33 matching lines @@
 
     d.dir(appPath, [
       d.dir('build', [
         d.dir('web', [
           d.file('foo.out', 'depeche')
         ])
       ])
     ]).validate();
   });
 }