Get rid of all the library tags.

lib/src/utils.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 yaml.utils;
-
 import 'package:source_span/source_span.dart';
 
 /// A pair of values.
 class Pair<E, F> {
   final E first;
   final F last;
 
   Pair(this.first, this.last);
 
   String toString() => '($first, $last)';
@@ skipping 18 matching lines @@
 /// emit a warning. To do so, it calls this callback. The default implementation
 /// prints a message using [print].
 YamlWarningCallback yamlWarningCallback = (message, [span]) {
   // TODO(nweiz): Print to stderr with color when issue 6943 is fixed and
   // dart:io is available.
   if (span != null) message = span.message(message);
   print(message);
 };