Remove more references to the old plugin system

pkg/analysis_server/lib/src/analysis_server.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 'dart:collection';
 import 'dart:core';
 import 'dart:io' as io;
 import 'dart:math' show max;
 
@@ skipping 50 matching lines @@
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:analyzer/src/generated/utilities_general.dart';
 import 'package:analyzer/src/util/glob.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart' hide Element;
 import 'package:front_end/src/base/performace_logger.dart';
 import 'package:front_end/src/byte_store/byte_store.dart';
 import 'package:front_end/src/byte_store/file_byte_store.dart';
-import 'package:plugin/plugin.dart';
 import 'package:telemetry/crash_reporting.dart';
 import 'package:telemetry/telemetry.dart' as telemetry;
 import 'package:watcher/watcher.dart';
 
 typedef void OptionUpdater(AnalysisOptionsImpl options);
 
 /**
  * Enum representing reasons why analysis might be done for a given file.
  */
 class AnalysisDoneReason {
@@ skipping 164 matching lines @@
    */
   final nd.FileContentOverlay fileContentOverlay = new nd.FileContentOverlay();
 
   /**
    * The current state of overlays from the client.  This is used as the
    * content cache for all contexts.
    */
   final ContentCache overlayState = new ContentCache();
 
   /**
-   * The plugins that are defined outside the analysis_server package.
-   */
-  List<Plugin> userDefinedPlugins;
-
-  /**
    * If the "analysis.analyzedFiles" notification is currently being subscribed
    * to (see [generalAnalysisServices]), and at least one such notification has
    * been sent since the subscription was enabled, the set of analyzed files
    * that was delivered in the most recently sent notification.  Otherwise
    * `null`.
    */
   Set<String> prevAnalyzedFiles;
 
   /**
    * The default options used to create new analysis contexts. This object is
@@ skipping 1251 matching lines @@
   /**
    * The [PerformanceTag] for time spent in server request handlers.
    */
   static PerformanceTag serverRequests = server.createChild('requests');
 
   /**
    * The [PerformanceTag] for time spent in split store microtasks.
    */
   static PerformanceTag splitStore = new PerformanceTag('splitStore');
 }