[libc++][NFC] Update namespace comments in include/

update the namspace comments in include/

Reviewed By: ldionne, #libc

Spies: smeenai, libcxx-commits

Differential Revision: https://reviews.llvm.org/D114947

NOKEYCHECK=True
GitOrigin-RevId: d2b0df35afb7184f5a68f67d6ed0c6230688df7f
diff --git a/include/new b/include/new
index 593af9d..be0d972 100644
--- a/include/new
+++ b/include/new
@@ -177,7 +177,7 @@
 inline constexpr destroying_delete_t destroying_delete{};
 #endif // _LIBCPP_STD_VER > 17
 
-}  // std
+} // namespace std
 
 #if defined(_LIBCPP_CXX03_LANG)
 #define _THROW_BAD_ALLOC throw(std::bad_alloc)