Get rid of all the library tags.

test/transformer/exclusion/exclude_asset_prefix_test.dart

 // Copyright (c) 2014, 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';
 import '../../serve/utils.dart';
 
 main() {
   integration("allows a directory prefix to exclude", () {
     serveBarback();
 
     d.dir(appPath, [
       d.pubspec({
@@ skipping 24 matching lines @@
 
     pubGet();
     pubServe();
     requestShouldSucceed("foo.out", "foo.out");
     requestShouldSucceed("bar.out", "bar.out");
     requestShouldSucceed("subbub/foo.out", "foo.out");
     requestShould404("sub/foo.out");
     endPubServe();
   });
 }