rm obsolete code

GUI/Model/Sample/ItemWithParticles.h

@@ -53,11 +53,6 @@ public:
 protected:
     ItemWithParticles(const QString& abundanceTooltip, const QString& positionTooltip);
 
-private:
-    //! Convenience method to return a rotation item from the contained transformation item.
-    //! nullptr, if no transformation item defined.
-    RotationItem* rotationItem() const;
-
     DoubleProperty m_abundance;
     VectorProperty m_position;
     SelectionProperty<RotationItem*> m_rotation;