Remove the old task model

pkg/analyzer/lib/src/task/html.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.task.html;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/context/cache.dart';
-import 'package:analyzer/src/generated/engine.dart' hide AnalysisTask;
+import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/plugin/engine_plugin.dart';
 import 'package:analyzer/src/task/general.dart';
 import 'package:analyzer/task/dart.dart';
 import 'package:analyzer/task/general.dart';
 import 'package:analyzer/task/html.dart';
 import 'package:analyzer/task/model.dart';
@@ skipping 369 matching lines @@
    * The content of the fragment.
    */
   final String content;
 
   /**
    * Initialize a newly created script fragment to have the given [offset] and
    * [content].
    */
   ScriptFragment(this.offset, this.line, this.column, this.content);
 }