C++17 compliance

Index: src/utils/dtor.h
--- src/utils/dtor.h.orig
+++ src/utils/dtor.h
@@ -30,7 +30,7 @@
 #include "localconsts.h"
 
 template<typename T>
-struct dtor final : public std::unary_function <T, void>
+struct dtor final
 {
     A_DEFAULT_COPY(dtor)
 
@@ -39,8 +39,7 @@ struct dtor final : public std::unary_function <T, voi
 };
 
 template<typename T1, typename T2>
-struct dtor<std::pair<T1, T2> > :
-public std::unary_function <std::pair<T1, T2>, void>
+struct dtor<std::pair<T1, T2> >
 {
     void operator()(std::pair<T1, T2> &pair)
     { delete pair.second; }
