Remove IKMarkerTask defaulted copy ctor

"Rule of three": if a copy ctor, copy assignment, or dtor are declared then all three should be

Author: adamkewley

OpenSim/Tools/IKMarkerTask.h

@@ -40,7 +40,6 @@ OpenSim_DECLARE_CONCRETE_OBJECT(IKMarkerTask, IKTask);
 
 public:
     IKMarkerTask() = default;
-    IKMarkerTask(const IKMarkerTask&) = default;
     //=============================================================================
 };  // END of class IKMarkerTask
 //=============================================================================