Remove library tags, they aren't needed

lib/runtime/messages_widget.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.
 
 /// This library displays [MessageSummary]s from the Dart Dev Compiler.
-library dev_compiler.messages;
 
 import 'dart:convert';
 import 'dart:html';
 
 import 'package:dev_compiler/src/summary.dart';
 import 'package:source_span/source_span.dart';
 
 main() async {
   await window.animationFrame;
   displayMessages(await HttpRequest.getString('messages.json'));
@@ skipping 104 matching lines @@
 class _Visitor extends RecursiveSummaryVisitor {
   final Map<String, List<MessageSummary>> messagesByLevel = {};
 
   @override
   void visitMessage(MessageSummary message) {
     var level = message.level.toLowerCase();
     messagesByLevel.putIfAbsent(level, () => []);
     messagesByLevel[level].add(message);
   }
 }