Remove uses of the old plugin model from the analysis server

pkg/analysis_server/lib/plugin/analysis/analysis_domain.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.
-
-/**
- * Support for client code that interacts with the analysis domain of an
- * analysis server.
- *
- * Plugins can gain access to the request handler that implements the analysis
- * domain in order to extend the functionality of that domain. The class
- * [AnalysisDomain] defines the API of the analysis domain that plugins can use.
- *
- * If a plugin is interested in gaining access to the analysis domain, it should
- * register a function by including code like the following in the plugin's
- * registerExtensions method:
- *
- *     AnalysisDomain analysisDomain;
- *
- *     @override
- *     void registerExtensions(RegisterExtension registerExtension) {
- *       ...
- *       registerExtension(
- *           SET_ANALYSIS_DOMAIN_EXTENSION_POINT_ID,
- *           (AnalysisDomain domain) => analysisDomain = domain);
- *       ...
- *     }
- */
-import 'package:analysis_server/src/plugin/server_plugin.dart';
-import 'package:plugin/plugin.dart';
-
-/**
- * The identifier of the extension point that allows plugins to get access to an
- * [AnalysisDomain]. The object used as an extension must be a
- * [SetAnalysisDomain].
- */
-final String SET_ANALYSIS_DOMAIN_EXTENSION_POINT_ID = Plugin.join(
-    ServerPlugin.UNIQUE_IDENTIFIER,
-    ServerPlugin.SET_ANALISYS_DOMAIN_EXTENSION_POINT);
-
-/**
- * A function that is invoked after the analysis domain has been created and is
- * initialized.
- */
-typedef void SetAnalysisDomain(AnalysisDomain domain);
-
-/**
- * An object that gives plugins access to the analysis domain of the analysis
- * server.
- *
- * Clients may not extend, implement or mix-in this class.
- */
-abstract class AnalysisDomain {}