[libc++] Remove dead code and unneeded C++03 specializations from type_traits

[ldionne]

LGTM if CI passes.

libcxx/include/type_traits

 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _T1, class _T2> struct _LIBCPP_TEMPLATE_VIS pair;
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS hash;
 
-template <bool> struct _MetaBase;
-template <>
-struct _MetaBase<true> {
-  template <template <class...> class _FirstFn, template <class...> class, class ..._Args>
-  using _SelectApplyImpl _LIBCPP_NODEBUG = _FirstFn<_Args...>;
-  template <class _First, class...>
-  using _FirstImpl _LIBCPP_NODEBUG = _First;
-  template <class, class _Second, class...>
-  using _SecondImpl _LIBCPP_NODEBUG = _Second;
-};
-
-template <>
-struct _MetaBase<false> {
-  template <template <class...> class, template <class...> class _SecondFn, class ..._Args>
-  using _SelectApplyImpl _LIBCPP_NODEBUG = _SecondFn<_Args...>;
-};
-
-template <class ..._Args>
-using _FirstType _LIBCPP_NODEBUG = typename _MetaBase<(sizeof...(_Args) >= 1)>::template _FirstImpl<_Args...>;
-template <class ..._Args>
-using _SecondType _LIBCPP_NODEBUG = typename _MetaBase<(sizeof...(_Args) >= 2)>::template _SecondImpl<_Args...>;
-
 template <template <class...> class _Func, class ..._Args>
 struct _Lazy : _Func<_Args...> {};
 
 // Member detector base
 
 template <template <class...> class _Templ, class ..._Args, class = _Templ<_Args...> >
 true_type __sfinae_test_impl(int);
 template <template <class...> class, class ...>

 { };
 #endif // !C++03
 
 // result_of
 
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS)
 template <class _Callable> class _LIBCPP_DEPRECATED_IN_CXX17 result_of;
 
-#ifndef _LIBCPP_CXX03_LANG
-
 template <class _Fp, class ..._Args>
 class _LIBCPP_TEMPLATE_VIS result_of<_Fp(_Args...)>
     : public __invoke_of<_Fp, _Args...>
 {
 };
 
-#else // C++03
-
-template <class _Fn, bool, bool>
-class __result_of
-{
-};
-
-template <class _Fn, class ..._Args>
-class __result_of<_Fn(_Args...), true, false>
-{
-public:
-    typedef decltype(declval<_Fn>()(declval<_Args>()...)) type;
-};
-
-template <class _MP, class _Tp, bool _IsMemberFunctionPtr>
-struct __result_of_mp;
-
-// member function pointer
-
-template <class _MP, class _Tp>
-struct __result_of_mp<_MP, _Tp, true>
-{
-    using type = typename __member_pointer_traits<_MP>::_ReturnType;
-};
-
-// member data pointer
-
-template <class _MP, class _Tp, bool>
-struct __result_of_mdp;
-
-template <class _Rp, class _Class, class _Tp>
-struct __result_of_mdp<_Rp _Class::*, _Tp, false>
-{
-    using type = typename __apply_cv<decltype(*declval<_Tp>()), _Rp>::type&;
-};
-
-template <class _Rp, class _Class, class _Tp>
-struct __result_of_mdp<_Rp _Class::*, _Tp, true>
-{
-    using type = typename __apply_cv<_Tp, _Rp>::type&;
-};
-
-template <class _Rp, class _Class, class _Tp>
-struct __result_of_mp<_Rp _Class::*, _Tp, false>
-    : public __result_of_mdp<_Rp _Class::*, _Tp,
-            is_base_of<_Class, typename remove_reference<_Tp>::type>::value>
-{
-};
-
-template <class _Fn, class _Tp>
-class __result_of<_Fn(_Tp), false, true>  // _Fn must be member pointer
-    : public __result_of_mp<typename remove_reference<_Fn>::type,
-                            _Tp,
-                            is_member_function_pointer<typename remove_reference<_Fn>::type>::value>
-{
-};
-
-template <class _Fn, class _Tp, class ..._Args>
-class __result_of<_Fn(_Tp, _Args...), false, true>  // _Fn must be member pointer
-    : public __result_of_mp<typename remove_reference<_Fn>::type,
-                            _Tp,
-                            is_member_function_pointer<typename remove_reference<_Fn>::type>::value>
-{
-};
-
-template <class _Fn, class ..._Args>
-class _LIBCPP_TEMPLATE_VIS result_of<_Fn(_Args...)>
-    : public __result_of<_Fn(_Args...),
-                         is_class<typename remove_reference<_Fn>::type>::value ||
-                         is_function<typename remove_pointer<typename remove_reference<_Fn>::type>::type>::value,
-                         is_member_pointer<typename remove_reference<_Fn>::type>::value
-                        >
-{
-};
-
-#endif // C++03
-
 #if _LIBCPP_STD_VER > 11
 template <class _Tp> using result_of_t _LIBCPP_DEPRECATED_IN_CXX17 = typename result_of<_Tp>::type;
 #endif // _LIBCPP_STD_VER > 11
 #endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS)
 
 // __swappable
 
 template <class _Tp> struct __is_swappable;