[api] Remove duplicate forward declaration

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 110 matching lines @@
 class Global;
 template<class K, class V, class T> class PersistentValueMap;
 template <class K, class V, class T>
 class PersistentValueMapBase;
 template <class K, class V, class T>
 class GlobalValueMap;
 template<class V, class T> class PersistentValueVector;
 template<class T, class P> class WeakCallbackObject;
 class FunctionTemplate;
 class ObjectTemplate;
-class Data;
 template<typename T> class FunctionCallbackInfo;
 template<typename T> class PropertyCallbackInfo;
 class StackTrace;
 class StackFrame;
 class Isolate;
 class CallHandlerHelper;
 class EscapableHandleScope;
 template<typename T> class ReturnValue;
 
 namespace internal {
@@ skipping 9761 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // INCLUDE_V8_H_