Replace classh : class_ inhertance with using, as suggested by @henryiii

#5542 (comment)

Author: rwgk

include/pybind11/pybind11.h

@@ -2378,10 +2378,7 @@ class class_ : public detail::generic_type {
 // Supports easier switching between py::class_<T> and py::class_<T, py::smart_holder>:
 // users can simply replace the `_` in `class_` with `h` or vice versa.
 template <typename type_, typename... options>
-class classh : public class_<type_, smart_holder, options...> {
-public:
-    using class_<type_, smart_holder, options...>::class_;
-};
+using classh = class_<type_, smart_holder, options...>;
 
 /// Binds an existing constructor taking arguments Args...
 template <typename... Args>