Fixed Canvas3D update after an object instance is deleted.

src/slic3r/GUI/GUI_ObjectList.cpp

@@ -946,7 +946,6 @@ bool ObjectList::del_subobject_from_object(const int obj_idx, const int idx, con
             return false;
         }
         (*m_objects)[obj_idx]->delete_instance(idx);
-        (*m_objects)[obj_idx]->reset_volumes_idxs();
     }
     else
         return false;