fix: _execute should be pure virtual

source/RobotAPI/libraries/skills/provider/SpecializedSkill.h

@@ -25,14 +25,8 @@ namespace armarx
             }
 
             /// Override this method with the actual implementation. The callback is for status updates to the calling instance
-            virtual Status _execute(const AronT& params, const CallbackT& callback = [](const aron::data::DictPtr& returnValue) { (void) returnValue; })
-            {
-                (void) params;
-
-                ARMARX_WARNING_S << "You have to override this method!";
-                return Status::Succeeded;
-            }
-
+            virtual Status _execute(const AronT& params, const CallbackT& callback = [](const aron::data::DictPtr& returnValue) { (void) returnValue; }) = 0;
+            
             /// Do not use anymore
             Status _execute(const aron::data::DictPtr& params, const CallbackT& callback = [](const aron::data::DictPtr& returnValue) { (void) returnValue; }) final
             {