Use DartEditBuilder to write types and remove dead code

pkg/analyzer_plugin/lib/utilities/change_builder/change_builder_dart.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/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
@@ skipping 208 matching lines @@
    *
    * If the [groupName] is not `null`, then the name of the type (including type
    * parameters) will be included as a region in the linked edit group with that
    * name. If the [groupName] is not `null` and [addSupertypeProposals] is
    * `true`, then all of the supertypes of the [type] will be added as
    * suggestions for alternatives to the type name.
    *
    * If a [methodBeingCopied] is provided, then type parameters defined by that
    * method are assumed to be part of what is being written and hence valid
    * types.
+   *
+   * Return `true` if some text was written.
    */
   bool writeType(DartType type,
       {bool addSupertypeProposals: false,
       String groupName,
       ExecutableElement methodBeingCopied,
       bool required: false});
 
   /**
    * Write the code to declare the given [typeParameter]. The enclosing angle
    * brackets are not automatically written.
@@ skipping 55 matching lines @@
  *
  * Clients may not extend, implement or mix-in this class.
  */
 abstract class DartLinkedEditBuilder implements LinkedEditBuilder {
   /**
    * Add the given [type] and all of its supertypes (other than mixins) as
    * suggestions for the current linked edit group.
    */
   void addSuperTypesAsSuggestions(DartType type);
 }