Remove more references to the old plugin system

pkg/analysis_server/lib/starter.dart

 // Copyright (c) 2015, 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 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/server/driver.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:analyzer/plugin/resolver_provider.dart';
-import 'package:plugin/plugin.dart';
 
 /**
  * An object that can be used to start an analysis server. This class exists so
  * that clients can configure an analysis server before starting it.
  *
  * Clients may not extend, implement or mix-in this class.
  */
 abstract class ServerStarter {
   /**
    * Initialize a newly created starter to start up an analysis server.
@@ skipping 13 matching lines @@
   void set instrumentationServer(InstrumentationServer server);
 
   /**
    * Set the package resolver provider used to override the way package URI's
    * are resolved in some contexts. The provider should return `null` if the
    * default package resolution scheme should be used instead.
    */
   void set packageResolverProvider(ResolverProvider provider);
 
   /**
-   * Set the [plugins] that are defined outside the analysis_server package.
-   */
-  void set userDefinedPlugins(List<Plugin> plugins);
-
-  /**
    * Use the given command-line [arguments] to start this server.
    *
    * At least temporarily returns AnalysisServer so that consumers of the
    * starter API can then use the server, this is done as a stopgap for the
    * angular plugin until the official plugin API is finished.
    */
   AnalysisServer start(List<String> arguments);
 }