Remove the old task model

pkg/analyzer/lib/src/context/cache.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.
 
 library analyzer.src.context.cache;
 
 import 'dart:async';
 import 'dart:collection';
 
-import 'package:analyzer/src/generated/engine.dart'
-    show AnalysisEngine, CacheState, InternalAnalysisContext, RetentionPriority;
+import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_collection.dart';
 import 'package:analyzer/src/task/model.dart';
 import 'package:analyzer/task/model.dart';
 
 /**
  * Return `true` if the given [target] is a priority one.
  */
 typedef bool IsPriorityAnalysisTarget(AnalysisTarget target);
@@ skipping 1234 matching lines @@
   void resultAccessed(TargetedResult result) {}
 
   @override
   List<TargetedResult> resultStored(TargetedResult newResult, newValue) {
     return TargetedResult.EMPTY_LIST;
   }
 
   @override
   void targetRemoved(AnalysisTarget target) {}
 }