Remove more libraries directives from server

pkg/analysis_server/lib/src/provisional/completion/dart/completion.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
  * Dart specific completion contributors.
  *
  * Plugins can register Dart specific completion contributor factories.
  * The registered contributor factories will be used to instantiate new
  * contributors to get completions any time a client issues
  * a 'completion.getSuggestions' request.
  *
  * If a plugin wants to add completions, it should implement
  * [DartCompletionContributorFactory] by including code
  * like the following in the plugin's registerExtensions method:
  *
  *     @override
  *     void registerExtensions(RegisterExtension registerExtension) {
  *       ...
  *       registerExtension(
  *           DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID,
  *           () => new MyDartCompletionContributor());
  *       ...
  *     }
  */
-library analysis_server.src.provisional.completion.dart;
-
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion_plugin.dart';
 import 'package:plugin/plugin.dart';
 
 /**
  * The identifier of the extension point that allows plugins to register code
  * completion contributors. The object used as an extension must be a
  * [DartCompletionContributorFactory].
  */
 final String DART_COMPLETION_CONTRIBUTOR_EXTENSION_POINT_ID = Plugin.join(
     DartCompletionPlugin.UNIQUE_IDENTIFIER,
     DartCompletionPlugin.CONTRIBUTOR_EXTENSION_POINT);