Revert "[walker] Try to warn if someone forgot to call walk()"

This reverts commit dd9bd39c3febe7141a0385a0976a3d026f099df9,
as it produces undesirable warnings if the walker was
appended to another walker.

dune/xt/grid/walker.hh

@@ -83,14 +83,12 @@ private:
 public:
   explicit Walker(GridViewType grd_vw)
     : grid_view_(grd_vw)
-    , user_decided_agains_clearing_of_functors_(false)
   {
   }
 
   Walker(const ThisType& other)
     : BaseType()
     , grid_view_(other.grid_view_)
-    , user_decided_agains_clearing_of_functors_(other.user_decided_agains_clearing_of_functors_)
   {
     // Since all Common::PerThreadValue are created with the same size given by the global singleton threadManage(),
     // we just assume they are of the same size!
@@ -123,20 +121,6 @@ public:
 
   ~Walker()
   {
-#ifndef DXT_DISABLE_WARNINGS
-    // Warn if there are functors left, since we assume someone forgot to walk()!
-    if (!user_decided_agains_clearing_of_functors_
-        && element_functor_wrappers_->size() + intersection_functor_wrappers_->size()
-                   + element_and_intersection_functor_wrappers_->size()
-               > 0) {
-      Common::TimedLogger().get("dune.xt.grid.walker").warn()
-          << "[warning when descructing Walker] there are still uncleared functors, which indicates that you forgot to "
-             "call walk()!"
-          << "\n"
-          << "(To disable this warning, #define DXT_DISABLE_WARNINGS at compile time or configure the TimedLogger at "
-             "runtime.)";
-    }
-#endif // DXT_DISABLE_WARNINGS
   } // ~Walker(...)
 
   const GridViewType& grid_view() const
@@ -420,7 +404,6 @@ public:
 
   void walk(const bool use_tbb = false, const bool clear_functors = true)
   {
-    user_decided_agains_clearing_of_functors_ = !clear_functors;
 #if HAVE_TBB
     if (use_tbb) {
       const auto num_partitions =
@@ -505,7 +488,6 @@ public:
   template <class PartioningType>
   void walk(PartioningType& partitioning, const bool clear_functors = true)
   {
-    user_decided_agains_clearing_of_functors_ = !clear_functors;
     // prepare functors
     prepare();
 
@@ -577,7 +559,6 @@ private:
   } // ... walk_range(...)
 
   GridViewType grid_view_;
-  bool user_decided_agains_clearing_of_functors_;
   Common::PerThreadValue<std::list<std::shared_ptr<internal::ElementFunctorWrapper<GridViewType>>>>
       element_functor_wrappers_;
   Common::PerThreadValue<std::list<std::shared_ptr<internal::IntersectionFunctorWrapper<GridViewType>>>>