[libc++][spaceship] P1612R2: Removed `operator!=` from `locale`

[H-G-Hristov]

Summary

Implemented parts of P1612R2:

• Removed operator!= from locale

[Mordante]

LGTM!

[H-G-Hristov]

Rebased

libcxx/docs/Status/SpaceshipProjects.csv

 "| `[time.zone.nonmembers] <https://wg21.link/time.zone.nonmembers>`_
 | `[time.zone.zonedtime.nonmembers] <https://wg21.link/time.zone.zonedtime.nonmembers>`_
 | `[time.zone.leap.nonmembers] <https://wg21.link/time.zone.leap.nonmembers>`_
 | `[time.zone.link.nonmembers] <https://wg21.link/time.zone.link.nonmembers>`_","| chrono::time_zone
 | chrono::leap_second
 | chrono::time_zone_link",A ``<chrono>`` implementation,Unassigned,|Not Started|
 - `5.13 Clause 28: Localization library <https://wg21.link/p1614r2#clause-28-localization-library>`_,,,,
 "| `[locale] <https://wg21.link/locale>`_
-| `[locale.operators] <https://wg21.link/locale.operators>`_",| remove ops `locale`,None,Unassigned,|Not Started|
+| `[locale.operators] <https://wg21.link/locale.operators>`_",| remove ops `locale <https://reviews.llvm.org/D152654>`_,None,Hristo Hristov,|Complete|
 - `5.14 Clause 29: Input/output library <https://wg21.link/p1614r2#clause-29-inputoutput-library>`_,,,,
 | `[fs.filesystem.syn] <https://wg21.link/fs.filesystem.syn>`_,| `filesystem::space_info <https://reviews.llvm.org/D130861>`_,None,Adrian Vogelsgesang,|Complete|
 "| `[fs.class.path] <https://wg21.link/fs.class.path>`_
 | `[fs.path.nonmember] <https://wg21.link/fs.path.nonmember>`_",| `filesystem::path <https://reviews.llvm.org/D130859>`_,None,Adrian Vogelsgesang,|Complete|
 | `[fs.class.file.status] <https://wg21.link/fs.class.file.status>`_,| `file_status <https://reviews.llvm.org/D152647>`_,None,Hristo Hristov,|Complete|
 "| `[fs.class.directory.entry] <https://wg21.link/fs.class.directory.entry>`_
 | `[fs.dir.entry.obs] <https://wg21.link/fs.dir.entry.obs>`_",| `filesystem::directory_entry <https://reviews.llvm.org/D130860>`_,None,Adrian Vogelsgesang,|Complete|
 - `5.15 Clause 30: Regular expressions library <https://wg21.link/p1614r2#clause-30-regular-expressions-library>`_,,,,

libcxx/include/__locale

public:
 
     template <class _Facet>
       _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
       locale combine(const locale&) const;
 
     // locale operations:
     string name() const;
     bool operator==(const locale&) const;
+#if _LIBCPP_STD_VER <= 17
     _LIBCPP_HIDE_FROM_ABI bool operator!=(const locale& __y) const {return !(*this == __y);}
+#endif
     template <class _CharT, class _Traits, class _Allocator>
       _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
       bool operator()(const basic_string<_CharT, _Traits, _Allocator>&,
                       const basic_string<_CharT, _Traits, _Allocator>&) const;
 
     // global locale objects:
     static locale global(const locale&);
     static const locale& classic();

libcxx/include/locale

public:
 
     const locale& operator=(const locale& other) noexcept;
 
     template <class Facet> locale combine(const locale& other) const;
 
     // locale operations:
     basic_string<char> name() const;
     bool operator==(const locale& other) const;
-    bool operator!=(const locale& other) const;
+    bool operator!=(const locale& other) const;                              // removed C++20
     template <class charT, class Traits, class Allocator>
       bool operator()(const basic_string<charT,Traits,Allocator>& s1,
                       const basic_string<charT,Traits,Allocator>& s2) const;
 
     // global locale objects:
     static locale global(const locale&);
     static const locale& classic();
 };