Get rid of all the library tags.

lib/src/frontend/on_platform.dart

 // Copyright (c) 2015, 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 test.frontend.on_platform;
-
 /// An annotation for platform-specific customizations for a test suite.
 ///
 /// See [the README][onPlatform].
 ///
 /// [onPlatform]: https://github.com/dart-lang/test/blob/master/README.md#platform-specific-configuration
 class OnPlatform {
   final Map<String, dynamic> annotationsByPlatform;
 
   const OnPlatform(this.annotationsByPlatform);
 }