[libcxx] fixes `common_reference` requirement for `swappable_with`

LWG3175 identifies that the `common_reference` requirement for
`swappable_with` is over-constraining and doesn't need to concern itself
with cv- or reference qualifiers.

Differential Revision: https://reviews.llvm.org/D99817

GitOrigin-RevId: cedd07df5136ba446be23dbd2ca7d29d7b82cd60
diff --git a/include/concepts b/include/concepts
index 200a177..6ce2fad 100644
--- a/include/concepts
+++ b/include/concepts
@@ -326,7 +326,7 @@
 
 template<class _Tp, class _Up>
 concept swappable_with =
-  common_reference_with<_Tp&, _Up&> &&
+  common_reference_with<_Tp, _Up> &&
   requires(_Tp&& __t, _Up&& __u) {
     ranges::swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Tp>(__t));
     ranges::swap(_VSTD::forward<_Up>(__u), _VSTD::forward<_Up>(__u));