Remove the old task model

pkg/analysis_server/lib/src/services/completion/dart_completion_manager.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.
 
 library services.completion.dart;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
     show AnalysisRequest, CompletionContributor, CompletionRequest;
 import 'package:analysis_server/src/provisional/completion/dart/completion_target.dart';
 import 'package:analysis_server/src/services/completion/arglist_contributor.dart';
 import 'package:analysis_server/src/services/completion/combinator_contributor.dart';
 import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/completion_manager.dart';
 import 'package:analysis_server/src/services/completion/dart/common_usage_sorter.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart'
     as newImpl;
 import 'package:analysis_server/src/services/completion/dart/contribution_sorter.dart';
 import 'package:analysis_server/src/services/completion/dart_completion_cache.dart';
 import 'package:analysis_server/src/services/completion/imported_reference_contributor.dart';
 import 'package:analysis_server/src/services/completion/local_reference_contributor.dart';
 import 'package:analysis_server/src/services/completion/optype.dart';
 import 'package:analysis_server/src/services/completion/prefixed_element_contributor.dart';
 import 'package:analysis_server/src/services/completion/uri_contributor.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/generated/ast.dart';
-import 'package:analyzer/src/generated/engine.dart' hide AnalysisContextImpl;
+import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/source.dart';
 
 export 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart'
     show
         DART_RELEVANCE_COMMON_USAGE,
         DART_RELEVANCE_DEFAULT,
         DART_RELEVANCE_HIGH,
         DART_RELEVANCE_INHERITED_ACCESSOR,
         DART_RELEVANCE_INHERITED_FIELD,
@@ skipping 406 matching lines @@
             parameterNames: suggestion.parameterNames,
             parameterTypes: suggestion.parameterTypes,
             requiredParameterCount: suggestion.requiredParameterCount,
             hasNamedParameters: suggestion.hasNamedParameters,
             returnType: suggestion.returnType,
             element: suggestion.element);
       }
     }
   }
 }