Remove more libraries directives from server

pkg/analysis_server/lib/plugin/analysis/occurrences/occurrences.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 extends the analysis server by adding new
  * occurrences contributors.
  *
  * Plugins can register occurrences contributors. The registered contributors
  * will be used to get occurrence information any time the server is about to
  * send an 'analysis.occurrences' notification.
  *
  * If a plugin wants to add occurrence information, it should implement the
  * class [OccurrencesContributor] and then register the contributor by including
  * code like the following in the plugin's registerExtensions method:
  *
  *     @override
  *     void registerExtensions(RegisterExtension registerExtension) {
  *       ...
  *       registerExtension(
  *           OCCURRENCES_CONTRIBUTOR_EXTENSION_POINT_ID,
  *           new MyOccurrencesContributor());
  *       ...
  *     }
  */
-library analysis_server.plugin.analysis.occurrences.occurrences;
-
 import 'package:analysis_server/plugin/analysis/occurrences/occurrences_core.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:plugin/plugin.dart';
 
 /**
  * The identifier of the extension point that allows plugins to register
  * occurrence information. The object used as an extension must be an
  * [OccurrencesContributor].
  */
 final String OCCURRENCES_CONTRIBUTOR_EXTENSION_POINT_ID = Plugin.join(
     ServerPlugin.UNIQUE_IDENTIFIER,
     ServerPlugin.OCCURRENCES_CONTRIBUTOR_EXTENSION_POINT);