[libc++][C++03] Remove code that is not used in C++03 (#134045)

This patch removes code which is guarded by `_LIBCPP_STD_VER` and
`_LIBCPP_CXX03_LANG`.

This is part of
https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc.

Author: philnik777

libcxx/include/__cxx03/__algorithm/equal.h

@@ -66,65 +66,6 @@ equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first
   return std::equal(__first1, __last1, __first2, __equal_to());
 }
 
-#if _LIBCPP_STD_VER >= 14
-
-template <class _Iter1, class _Sent1, class _Iter2, class _Sent2, class _Pred, class _Proj1, class _Proj2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_impl(
-    _Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2, _Pred& __comp, _Proj1& __proj1, _Proj2& __proj2) {
-  while (__first1 != __last1 && __first2 != __last2) {
-    if (!std::__invoke(__comp, std::__invoke(__proj1, *__first1), std::__invoke(__proj2, *__first2)))
-      return false;
-    ++__first1;
-    ++__first2;
-  }
-  return __first1 == __last1 && __first2 == __last2;
-}
-
-template <class _Tp,
-          class _Up,
-          class _Pred,
-          class _Proj1,
-          class _Proj2,
-          __enable_if_t<__desugars_to_v<__equal_tag, _Pred, _Tp, _Up> && __is_identity<_Proj1>::value &&
-                            __is_identity<_Proj2>::value && !is_volatile<_Tp>::value && !is_volatile<_Up>::value &&
-                            __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
-                        int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
-__equal_impl(_Tp* __first1, _Tp* __last1, _Up* __first2, _Up*, _Pred&, _Proj1&, _Proj2&) {
-  return std::__constexpr_memcmp_equal(__first1, __first2, __element_count(__last1 - __first1));
-}
-
-template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
-equal(_InputIterator1 __first1,
-      _InputIterator1 __last1,
-      _InputIterator2 __first2,
-      _InputIterator2 __last2,
-      _BinaryPredicate __pred) {
-  if constexpr (__has_random_access_iterator_category<_InputIterator1>::value &&
-                __has_random_access_iterator_category<_InputIterator2>::value) {
-    if (std::distance(__first1, __last1) != std::distance(__first2, __last2))
-      return false;
-  }
-  __identity __proj;
-  return std::__equal_impl(
-      std::__unwrap_iter(__first1),
-      std::__unwrap_iter(__last1),
-      std::__unwrap_iter(__first2),
-      std::__unwrap_iter(__last2),
-      __pred,
-      __proj,
-      __proj);
-}
-
-template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
-equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
-  return std::equal(__first1, __last1, __first2, __last2, __equal_to());
-}
-
-#endif // _LIBCPP_STD_VER >= 14
-
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS

libcxx/include/__cxx03/__algorithm/for_each.h

@@ -33,21 +33,6 @@ for_each(_InputIterator __first, _InputIterator __last, _Function __f) {
   return __f;
 }
 
-// __movable_box is available in C++20, but is actually a copyable-box, so optimization is only correct in C++23
-#if _LIBCPP_STD_VER >= 23
-template <class _SegmentedIterator, class _Function>
-  requires __is_segmented_iterator<_SegmentedIterator>::value
-_LIBCPP_HIDE_FROM_ABI constexpr _Function
-for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Function __func) {
-  ranges::__movable_box<_Function> __wrapped_func(in_place, std::move(__func));
-  std::__for_each_segment(__first, __last, [&](auto __lfirst, auto __llast) {
-    __wrapped_func =
-        ranges::__movable_box<_Function>(in_place, std::for_each(__lfirst, __llast, std::move(*__wrapped_func)));
-  });
-  return std::move(*__wrapped_func);
-}
-#endif // _LIBCPP_STD_VER >= 23
-
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS