Remove library tags, they aren't needed

lib/src/runner/file_utils.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.
 
 /// File-listing utils used by dartdevrun.
-library dev_compiler.src.runner.file_utils;
 
 import 'dart:async';
 import 'dart:io';
 
 Future<List<File>> listJsFiles(Directory dir) async {
   var list = [];
   await for (var file in dir.list(recursive: true, followLinks: true)) {
     if (file is File && file.path.endsWith(".js")) list.add(file.absolute);
   }
   return list;
 }