compressed_pair: cleanup

src/entt/core/compressed_pair.hpp

@@ -18,8 +18,7 @@ struct compressed_pair_element {
     using reference = Type &;
     using const_reference = const Type &;
 
-    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<Type>>>
-    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>) {}
+    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<Type>) = default;
 
     template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
     constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<Type, Arg>)
@@ -47,9 +46,7 @@ struct compressed_pair_element<Type, Tag, std::enable_if_t<is_ebco_eligible_v<Ty
     using const_reference = const Type &;
     using base_type = Type;
 
-    template<bool Dummy = true, typename = std::enable_if_t<Dummy && std::is_default_constructible_v<base_type>>>
-    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>)
-        : base_type{} {}
+    constexpr compressed_pair_element() noexcept(std::is_nothrow_default_constructible_v<base_type>) = default;
 
     template<typename Arg, typename = std::enable_if_t<!std::is_same_v<std::remove_cv_t<std::remove_reference_t<Arg>>, compressed_pair_element>>>
     constexpr compressed_pair_element(Arg &&arg) noexcept(std::is_nothrow_constructible_v<base_type, Arg>)