Remove unused setter from ServerStarter and un-deprecate a used setter

pkg/analysis_server/test/socket_server_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.
 
 library test.socket.server;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
@@ skipping 98 matching lines @@
 
   static SocketServer _createSocketServer() {
     ServerPlugin serverPlugin = new ServerPlugin();
     ExtensionManager manager = new ExtensionManager();
     manager.processPlugins([serverPlugin]);
     return new SocketServer(
         new AnalysisServerOptions(),
         DirectoryBasedDartSdk.defaultSdk,
         InstrumentationService.NULL_SERVICE,
         serverPlugin,
-        null,
         null);
   }
 }
 
 class _MockRequestHandler implements RequestHandler {
   final bool futureException;
 
   _MockRequestHandler(this.futureException);
 
   @override
   Response handleRequest(Request request) {
     if (futureException) {
       new Future(throwException);
       return new Response(request.id);
     }
     throw 'mock request exception';
   }
 
   void throwException() {
     throw 'mock future exception';
   }
 }