Remove the old task model

pkg/analyzer/test/src/task/driver_test.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 test.src.task.driver_test;
 
 import 'package:analyzer/src/context/cache.dart';
-import 'package:analyzer/src/generated/engine.dart'
-    hide
-        AnalysisCache,
-        AnalysisContextImpl,
-        AnalysisTask,
-        UniversalCachePartition,
-        WorkManager;
+import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/task/driver.dart';
 import 'package:analyzer/src/task/inputs.dart';
 import 'package:analyzer/src/task/manager.dart';
 import 'package:analyzer/task/model.dart';
 import 'package:typed_mock/typed_mock.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../generated/test_support.dart';
 import '../../reflective_tests.dart';
@@ skipping 759 matching lines @@
         return dependency;
       }
     }
     return null;
   }
 }
 
 class _WorkManagerMock extends TypedMock implements WorkManager {
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }