clean out smart_holder_type_casters-related code

include/pybind11/cast.h

@@ -69,7 +69,7 @@ class type_caster_enum_type {
         if (native_enum) {
             return native_enum(static_cast<Underlying>(src)).release();
         }
-        return type_caster_for_class_<EnumType>::cast(
+        return type_caster_base<EnumType>::cast(
             std::forward<SrcType>(src),
             // Fixes https://github.com/pybind/pybind11/pull/3643#issuecomment-1022987818:
             return_value_policy::copy,
@@ -91,7 +91,7 @@ class type_caster_enum_type {
             return true;
         }
         if (!pybind11_enum_) {
-            pybind11_enum_.reset(new type_caster_for_class_<EnumType>());
+            pybind11_enum_.reset(new type_caster_base<EnumType>());
         }
         return pybind11_enum_->load(src, convert);
     }
@@ -116,7 +116,7 @@ class type_caster_enum_type {
     }
 
 private:
-    std::unique_ptr<type_caster_for_class_<EnumType>> pybind11_enum_;
+    std::unique_ptr<type_caster_base<EnumType>> pybind11_enum_;
     EnumType value;
 };
 
@@ -133,27 +133,6 @@ template <typename EnumType>
 class type_caster<EnumType, detail::enable_if_t<type_uses_type_caster_enum_type<EnumType>::value>>
     : public type_caster_enum_type<EnumType> {};
 
-template <typename T>
-struct type_uses_smart_holder_type_caster {
-    static constexpr bool value
-        = std::is_base_of<smart_holder_type_caster_base_tag, make_caster<T>>::value
-#ifdef PYBIND11_USE_SMART_HOLDER_AS_DEFAULT
-          || type_uses_type_caster_enum_type<T>::value
-#endif
-        ;
-};
-
-template <typename T, typename SFINAE = void>
-struct type_caster_classh_enum_aware : type_caster<T> {};
-
-#ifdef PYBIND11_USE_SMART_HOLDER_AS_DEFAULT
-template <typename EnumType>
-struct type_caster_classh_enum_aware<
-    EnumType,
-    detail::enable_if_t<type_uses_type_caster_enum_type<EnumType>::value>>
-    : type_caster_for_class_<EnumType> {};
-#endif
-
 template <typename T, detail::enable_if_t<std::is_enum<T>::value, int> = 0>
 bool isinstance_native_enum_impl(handle obj, const std::type_info &tp) {
     handle native_enum = global_internals_native_enum_type_map_get_item(tp);