[libc++][spaceship] Removes unneeded relational operators. (#100441)

This is a followup of #99343.
Since that patch was quite late in the LLVM-19 release cycle some of the
unneeded relational operator were not removed in C++20.

This removes them and gives the change a bit more "baking" time, just in
case there are issues with this change in user code. This change is
intended to be an NFC.

Author: mordante

libcxx/include/__iterator/bounded_iter.h

@@ -209,9 +209,7 @@ struct __bounded_iter {
   operator!=(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
     return __x.__current_ != __y.__current_;
   }
-#endif
 
-  // TODO(mordante) disable these overloads in the LLVM 20 release.
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
   operator<(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
     return __x.__current_ < __y.__current_;
@@ -229,7 +227,7 @@ struct __bounded_iter {
     return __x.__current_ >= __y.__current_;
   }
 
-#if _LIBCPP_STD_VER >= 20
+#else
   _LIBCPP_HIDE_FROM_ABI constexpr friend strong_ordering
   operator<=>(__bounded_iter const& __x, __bounded_iter const& __y) noexcept {
     if constexpr (three_way_comparable<_Iterator, strong_ordering>) {

libcxx/include/__iterator/wrap_iter.h

@@ -145,9 +145,6 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bool
 operator!=(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) _NOEXCEPT {
   return !(__x == __y);
 }
-#endif
-
-// TODO(mordante) disable these overloads in the LLVM 20 release.
 template <class _Iter1>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bool
 operator>(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter1>& __y) _NOEXCEPT {
@@ -184,7 +181,7 @@ operator<=(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) _NOEX
   return !(__y < __x);
 }
 
-#if _LIBCPP_STD_VER >= 20
+#else
 template <class _Iter1, class _Iter2>
 _LIBCPP_HIDE_FROM_ABI constexpr strong_ordering
 operator<=>(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) noexcept {

libcxx/include/deque

@@ -380,9 +380,6 @@ public:
   _LIBCPP_HIDE_FROM_ABI friend bool operator!=(const __deque_iterator& __x, const __deque_iterator& __y) {
     return !(__x == __y);
   }
-#endif
-
-  // TODO(mordante) disable these overloads in the LLVM 20 release.
   _LIBCPP_HIDE_FROM_ABI friend bool operator<(const __deque_iterator& __x, const __deque_iterator& __y) {
     return __x.__m_iter_ < __y.__m_iter_ || (__x.__m_iter_ == __y.__m_iter_ && __x.__ptr_ < __y.__ptr_);
   }
@@ -399,7 +396,8 @@ public:
     return !(__x < __y);
   }
 
-#if _LIBCPP_STD_VER >= 20
+#else
+
   _LIBCPP_HIDE_FROM_ABI friend strong_ordering operator<=>(const __deque_iterator& __x, const __deque_iterator& __y) {
     if (__x.__m_iter_ < __y.__m_iter_)
       return strong_ordering::less;