add remove_cvptr

like remove_cvref
remove_cvptr.hpp
```
// Distributed under the Boost Software License Version 1.0 https://www.boost.org/LICENSE_1_0.txt
// Copyright Gero Peterhoff

#ifndef BOOST_TYPE_TRAITS_REMOVE_CVPTR_HPP
#define BOOST_TYPE_TRAITS_REMOVE_CVPTR_HPP

#include
#include

namespace boost
{
template
struct remove_cvptr
{
typedef typename remove_cv::type>::type type;
};

#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
template using remove_cvptr_t = typename remove_cvptr::type;
#endif
} // boost

#endif // BOOST_TYPE_TRAITS_REMOVE_CVPTR_HPP
```