Merge branch 'feature/deprecated-void-t' into 'master'

Remove 'Dune::void_t' in favor of simple concept check

See merge request extensions/dune-vtk!26

dune/vtk/localfunction.hh

@@ -26,7 +26,7 @@ namespace Dune
       using LocalCoordinate = typename Entity::Geometry::LocalCoordinate;
 
       template <class LF, class E>
-      using HasBind = decltype(std::declval<LF>().bind(std::declval<E>()));
+      using HasBind = decltype((std::declval<LF>().bind(std::declval<E>()), true));
 
     private:
       struct RangeProxy
@@ -62,7 +62,7 @@ namespace Dune
       /// Construct the Vtk::LocalFunction from any function object that has a bind(element) method.
       template <class LF,
         disableCopyMove<Self, LF> = 0,
-        class = void_t<HasBind<LF,Entity>> >
+        HasBind<LF,Entity> = true>
       explicit LocalFunction (LF&& lf)
         : localFct_(std::make_shared<LocalFunctionWrapper<GridView,LF>>(std::forward<LF>(lf)))
       {}