Remove more references to the old plugin system

pkg/analysis_server/test/services/correction/assist_test.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.
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
 import 'package:analysis_server/src/services/correction/assist_internal.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/source/package_map_resolver.dart';
 import 'package:analyzer/src/dart/analysis/ast_provider_driver.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/dart/element/ast_provider.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/utilities/assist/assist.dart';
 import 'package:plugin/manager.dart';
-import 'package:plugin/plugin.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../../abstract_single_unit.dart';
 import 'flutter_util.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(AssistProcessorTest);
   });
@@ skipping 67 matching lines @@
   }
 
   List<LinkedEditSuggestion> expectedSuggestions(
       LinkedEditSuggestionKind kind, List<String> values) {
     return values.map((value) {
       return new LinkedEditSuggestion(value, kind);
     }).toList();
   }
 
   void processRequiredPlugins() {
-    List<Plugin> plugins = <Plugin>[];
-    plugins.addAll(AnalysisEngine.instance.requiredPlugins);
-
     ExtensionManager manager = new ExtensionManager();
-    manager.processPlugins(plugins);
+    manager.processPlugins(AnalysisEngine.instance.requiredPlugins);
   }
 
   void setUp() {
     super.setUp();
     offset = 0;
     length = 0;
   }
 
   test_addTypeAnnotation_BAD_privateType_closureParameter() async {
     addSource('/my_lib.dart', '''
@@ skipping 4269 matching lines @@
 
   @override
   final AstProvider astProvider;
 
   @override
   final CompilationUnit unit;
 
   _DartAssistContextForValues(this.source, this.selectionOffset,
       this.selectionLength, this.analysisDriver, this.astProvider, this.unit);
 }