[libc++][locale] Removes an transitive include.

Removes <cstdarg> transitive include from <locale> in C++23.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D133254

NOKEYCHECK=True
GitOrigin-RevId: ab7b776cf9570fe9ee78a4b86a834daa6e08dc69
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 9831d03..9c46642 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -53,7 +53,7 @@
 
   - C++20: ``chrono``
   - C++2b: ``algorithm``, ``array``, ``atomic``, ``bit``, ``chrono``,
-    ``climits``, ``cmath``, ``compare``, ``concepts``, ``cstdlib``,
+    ``climits``, ``cmath``, ``compare``, ``concepts``, ``cstdarg``, ``cstdlib``,
     ``cstring``, ``ctime``, ``exception``, ``functional``,
     ``initializer_list``, ``iosfwd``, ``iterator``, ``memory``, ``new``,
     ``optional``, ``ratio``, ``stdexcept``, ``tuple``, ``typeinfo``,