Remove uses of the old plugin model from the analysis server

pkg/analysis_server/test/edit/assists_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/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analysis_server/src/plugin/plugin_manager.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart' as plugin;
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/protocol/protocol_generated.dart' as plugin;
 import 'package:analyzer_plugin/src/protocol/protocol_internal.dart' as plugin;
-import 'package:plugin/manager.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../analysis_abstract.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(AssistsTest);
   });
 }
@@ skipping 12 matching lines @@
         new EditGetAssistsParams(testFile, offset, length).toRequest('0');
     Response response = await waitResponse(request);
     var result = new EditGetAssistsResult.fromResponse(response);
     changes = result.assists;
   }
 
   @override
   void setUp() {
     super.setUp();
     createProject();
-    ExtensionManager manager = new ExtensionManager();
-    manager.processPlugins([server.serverPlugin]);
     handler = new EditDomainHandler(server);
   }
 
   test_fromPlugins() async {
     PluginInfo info = new DiscoveredPluginInfo('a', 'b', 'c', null, null);
     String message = 'From a plugin';
     plugin.PrioritizedSourceChange change = new plugin.PrioritizedSourceChange(
         5,
         new SourceChange(message, edits: <SourceFileEdit>[
           new SourceFileEdit('', 0,
@@ skipping 68 matching lines @@
       if (change.message == message) {
         String resultCode =
             SourceEdit.applySequence(testCode, change.edits[0].edits);
         expect(resultCode, expectedCode);
         return;
       }
     }
     fail("Expected to find |$message| in\n" + changes.join('\n'));
   }
 }