Clean up some hints

pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_core.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/src/utilities/change_builder/change_builder_core.dart';
-import 'package:meta/meta.dart';
 
 /**
  * A builder used to build a [SourceChange].
  *
  * Clients may not extend, implement or mix-in this class.
  */
 abstract class ChangeBuilder {
   /**
    * Initialize a newly created change builder.
    */
@@ skipping 156 matching lines @@
    * Add the given [string] to the content of the current edit.
    */
   void write(String string);
 
   /**
    * Add the given [string] to the content of the current edit and then add an
    * end-of-line marker.
    */
   void writeln([String string]);
 }