Removed type_trait_aliases.hpp

Most of what used to be in these files (the _t types) were removed once we switched to C++14.
These two value aliases aren't used, so no need to keep them around.

src/utils/type_trait_aliases.hpp

@@ -1,44 +0,0 @@
-/*
-   Copyright (C) 2017-2018 by the Battle for Wesnoth Project https://www.wesnoth.org/
-
-   This program is free software; you can redistribute it and/or modify
-   it under the terms of the GNU General Public License as published by
-   the Free Software Foundation; either version 2 of the License, or
-   (at your option) any later version.
-   This program is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY.
-
-   See the COPYING file for more details.
-*/
-
-#pragma once
-
-#include "global.hpp"
-
-#include <type_traits>
-
-namespace utils
-{
-//
-// These aliases are part of the standard starting with C++17.
-// However, MSVC includes them as of VS 2015 Update 2, and they can also be implemented
-// using variable templates in C++14.
-//
-#ifdef HAVE_CXX17 || defined(_MSC_VER) && _MSC_VER >= 1900
-
-using std::is_base_of_v;
-using std::is_same_v;
-
-#else
-
-// is_base_of
-template<typename Base, typename Derived>
-static constexpr bool is_base_of_v = std::is_base_of<Base, Derived>::value;
-
-// is_same
-template<typename T, typename U>
-static constexpr bool is_same_v = std::is_same<T, U>::value;
-
-#endif // HAVE_CXX17
-
-} // end namespace utils