Get rid of all the library tags.

test/downgrade/does_not_show_other_versions_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.
 
-library pub_tests;
-
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   integration("does not show how many other versions are available", () {
     servePackages((builder) {
       builder.serve("downgraded", "1.0.0");
       builder.serve("downgraded", "2.0.0");
       builder.serve("downgraded", "3.0.0-dev");
     });
 
     d.appDir({
       "downgraded": "3.0.0-dev"
     }).create();
 
     pubGet();
 
     // Loosen the constraints.
     d.appDir({
       "downgraded": ">=2.0.0"
     }).create();
 
     pubDowngrade(output: contains("downgraded 2.0.0 (was 3.0.0-dev)"));
   });
 }