Fix analyzer_experimental hints: remove unused imports.

pkg/analyzer_experimental/example/parser_driver.dart

 #!/usr/bin/env dart
 
 // Copyright (c) 2013, 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.
 
 import 'package:analyzer_experimental/src/generated/ast.dart';
 import 'package:analyzer_experimental/src/generated/error.dart';
-import 'package:analyzer_experimental/src/generated/java_core.dart';
 import 'package:analyzer_experimental/src/generated/parser.dart';
 import 'package:analyzer_experimental/src/generated/scanner.dart';
 
 import 'dart:io';
 
 
 main() {
 
   print('working dir ${new File('.').fullPathSync()}');
 
@@ skipping 31 matching lines @@
   onError(error) => errors.add(error);
 }
 
 class _ASTVisitor extends GeneralizingASTVisitor {
   visitNode(ASTNode node) {
     print('${node.runtimeType} : <"${node.toString()}">');
     return super.visitNode(node);
   }
 }