Remove remaining opt-outs to 2.9 from analysis_server_client.

Change-Id: I4d971ef7cbc433894b4219f3e942eef40db24a60
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/194010
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server_client/test/all.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.
 
-// @dart = 2.9
-
 import 'live_test.dart' as live;
 import 'server_test.dart' as server;
 import 'verify_sorted_test.dart' as verify_sorted;

pkg/analysis_server_client/test/verify_sorted_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.
 
-// @dart = 2.9
-
 import 'package:analysis_server/src/services/correction/sort_members.dart';
 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/dart/analysis/results.dart';