Avoid use of std::iterator which is deprecated in C++17

source/Lib/CommonLib/Unit.h

@@ -817,7 +817,7 @@ private:
 #include <iterator>
 
 template<typename T>
-class UnitIterator : public std::iterator<std::forward_iterator_tag, T>
+class UnitIterator
 {
 private:
   T* m_punit;