Remove unused Visitor template

include/helpers.hpp

@@ -82,12 +82,4 @@ static inline int clz(unsigned int x) {
 // For lack of <ranges>, this adds some more brevity
 #define RANGE(s) std::begin(s), std::end(s)
 
-// Convenience feature for visiting variants.
-template<typename... Ts>
-struct Visitor : Ts... {
-	using Ts::operator()...;
-};
-template<typename... Ts>
-Visitor(Ts...) -> Visitor<Ts...>;
-
 #endif // HELPERS_H