Remove dead code for an unused (old) task

pkg/analyzer/test/generated/engine_test.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.engine_test;
 
 import 'dart:async';
@@ skipping 15 matching lines @@
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/sdk_io.dart';
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:analyzer/src/generated/testing/ast_factory.dart';
 import 'package:analyzer/src/generated/testing/element_factory.dart';
 import 'package:analyzer/src/generated/utilities_collection.dart';
 import 'package:analyzer/src/services/lint.dart';
 import 'package:analyzer/src/string_source.dart';
-import 'package:analyzer/src/task/task_dart.dart';
 import 'package:analyzer/task/model.dart' hide AnalysisTask;
 import 'package:html/dom.dart' show Document;
 import 'package:path/path.dart' as pathos;
 import 'package:typed_mock/typed_mock.dart';
 import 'package:unittest/unittest.dart';
 import 'package:watcher/src/utils.dart';
 
 import '../reflective_tests.dart';
 import 'all_the_rest_test.dart';
 import 'resolver_test.dart';
@@ skipping 6328 matching lines @@
   }
 }
 
 /**
  * Instances of the class `TestTaskVisitor` implement a task visitor that fails if any of its
  * methods are invoked. Subclasses typically override the expected methods to not cause a test
  * failure.
  */
 class TestTaskVisitor<E> implements AnalysisTaskVisitor<E> {
   @override
-  E visitBuildUnitElementTask(BuildUnitElementTask task) {
-    fail("Unexpectedly invoked visitGenerateDartErrorsTask");
-    return null;
-  }
-
-  @override
   E visitGenerateDartErrorsTask(GenerateDartErrorsTask task) {
     fail("Unexpectedly invoked visitGenerateDartErrorsTask");
     return null;
   }
   @override
   E visitGenerateDartHintsTask(GenerateDartHintsTask task) {
     fail("Unexpectedly invoked visitGenerateDartHintsTask");
     return null;
   }
   @override
@@ skipping 234 matching lines @@
   @override
   bool exists() => true;
 }
 
 class _UniversalCachePartitionTest_test_setMaxCacheSize
     implements CacheRetentionPolicy {
   @override
   RetentionPriority getAstPriority(Source source, SourceEntry sourceEntry) =>
       RetentionPriority.LOW;
 }