[cleanup] Use concept check result directly

Since Dune::models() does now directly return an
std::integral_constant<bool,*> we can directly use
its result in ifElse().

dune/solvers/common/resize.hh

@@ -54,9 +54,7 @@ void resizeInitialize(TargetVector& x, const Vector& y, const Value& value)
   namespace H = Dune::Hybrid;
   auto size = H::size(y);
 
-//  H::ifElse(models<Concept::HasResize, TargetVector>(), [&](auto&& id) {
-  auto hasResize = std::integral_constant<bool, models<Concept::HasResize, TargetVector>()>();
-  H::ifElse(hasResize, [&](auto&& id) {
+  H::ifElse(models<Concept::HasResize, TargetVector>(), [&](auto&& id) {
       id(x).resize(size);
   }, [&](auto&& id) {
     if (H::size(x) != size)