remove GLModel from base class

- only 2 gizmo use cone

(cherry picked from commit prusa3d/PrusaSlicer@3c7390e34e)
(cherry picked from commit 4647fc49ef5b925432e087252f32a6601d0410da)

src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp

@@ -43,6 +43,8 @@ private:
     mutable float m_snap_fine_in_radius;
     mutable float m_snap_fine_out_radius;
 
+    GLModel m_cone;
+
 public:
     GLGizmoRotate(GLCanvas3D& parent, Axis axis);
     GLGizmoRotate(const GLGizmoRotate& other);