[element model] remove unnecessary analyzer_use_new_elements ignore

Change-Id: Id2a50c825ce94408a99f91602c3e9e05ef22b93c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/404342
Auto-Submit: Phil Quitslund <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>

Author: pq

pkg/analyzer/test/src/dart/element/least_upper_bound_helper_test.dart

@@ -2,8 +2,6 @@
 // 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.
 
-// ignore_for_file: analyzer_use_new_elements
-
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/least_upper_bound.dart';