remove useless header files

source/core/XTensorFunction.h

-/* NiuTrans.Tensor - an open-source tensor library
- * Copyright (C) 2017, Natural Language Processing Lab, Northestern University. 
- * All rights reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *   http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-/*
-* $Created by: XIAO Tong (email: xiaotong@mail.neu.edu.cn) 2018-04-24
-*/
-
-/* this is a class wrapper of tensor functions */
-
-#ifndef __XTENSORCORE_H__
-#define __XTENSORCORE_H__
-
-namespace nts{ // namespace nts(NiuTrans.Tensor)
-
-#include "../XTensor.h"
-#include "CHeader.h"
-
-/* tensor functions */
-class XTensorFunction
-{
-public:
-};
-
-} // namespace nts(NiuTrans.Tensor)
-
-#endif // __XTENSORCORE_H__
\ No newline at end of file