Remove Element.users support.

pkg/analyzer/lib/src/generated/resolver.dart

 // Copyright (c) 2014, 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 engine.resolver;
 
 import "dart:math" as math;
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/utilities_collection.dart';
-import 'package:analyzer/src/generated/visitors.dart';
 
 import 'ast.dart';
 import 'constant.dart';
 import 'element.dart';
 import 'element_resolver.dart';
 import 'engine.dart';
 import 'error.dart';
 import 'error_verifier.dart';
 import 'html.dart' as ht;
 import 'java_core.dart';
@@ skipping 15437 matching lines @@
    * library.
    */
   final HashSet<String> members = new HashSet<String>();
 
   /**
    * Names of resolved or unresolved class members that are read in the
    * library.
    */
   final HashSet<String> readMembers = new HashSet<String>();
 }