[oneDPL][ranges] revert unnecessary changes in iterator_defs.h

include/oneapi/dpl/pstl/iterator_defs.h

@@ -31,18 +31,23 @@ namespace __internal
 // SFINAE with a non-iterator type by providing a default value.
 template <typename _IteratorTag, typename... _IteratorTypes>
 auto
-__is_iterator_of(int) -> typename ::std::conjunction<::std::is_base_of<
-    _IteratorTag, typename ::std::iterator_traits<::std::decay_t<_IteratorTypes>>::iterator_category>...>::type;
+__is_iterator_of(int) -> decltype(
+    ::std::conjunction<::std::is_base_of<
+        _IteratorTag, typename ::std::iterator_traits<::std::decay_t<_IteratorTypes>>::iterator_category>...>{});
 
 template <typename... _IteratorTypes>
 auto
 __is_iterator_of(...) -> ::std::false_type;
 
 template <typename... _IteratorTypes>
-using __is_random_access_iterator = decltype(__is_iterator_of<::std::random_access_iterator_tag, _IteratorTypes...>(0));
+struct __is_random_access_iterator : decltype(__is_iterator_of<::std::random_access_iterator_tag, _IteratorTypes...>(0))
+{
+};
 
 template <typename... _IteratorTypes>
-using __is_forward_iterator = decltype(__is_iterator_of<::std::forward_iterator_tag, _IteratorTypes...>(0));
+struct __is_forward_iterator : decltype(__is_iterator_of<::std::forward_iterator_tag, _IteratorTypes...>(0))
+{
+};
 
 template <typename... _IteratorTypes>
 inline constexpr bool __is_random_access_iterator_v = __is_random_access_iterator<_IteratorTypes...>::value;