Remove unused imports missed in earlier CL

pkg/analysis_server/lib/src/services/completion/dart/completion_manager.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.
 
 import 'dart:async';
 
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
     show CompletionContributor, CompletionRequest;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/completion_core.dart';
@@ skipping 11 matching lines @@
 import 'package:analysis_server/src/services/completion/dart/library_prefix_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/local_constructor_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/local_library_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/local_reference_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/named_constructor_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/static_member_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/type_member_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/uri_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/variable_name_contributor.dart';
 import 'package:analyzer/dart/ast/ast.dart';
-import 'package:analyzer/dart/ast/standard_ast_factory.dart';
-import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
-import 'package:analyzer/src/dart/ast/token.dart';
 import 'package:analyzer/src/generated/engine.dart' hide AnalysisResult;
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/task/model.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/src/utilities/completion/completion_target.dart';
 import 'package:analyzer_plugin/src/utilities/completion/optype.dart';
 
 /**
  * [DartCompletionManager] determines if a completion request is Dart specific
  * and forwards those requests to all [DartCompletionContributor]s.
@@ skipping 223 matching lines @@
         request.source,
         request.offset,
         unit,
         request,
         performance);
 
     performance.logElapseTime(BUILD_REQUEST_TAG);
     return dartRequest;
   }
 }