__init__.py

def unregister():
    for c in classes:
        bpy.utils.unregister_class(c)
    for f in extension_panel_unregister_functors:
        f()
    extension_panel_unregister_functors.clear()

    # bpy.utils.unregister_module(__name__)

    # remove from the export / import menu
    bpy.types.TOPBAR_MT_file_export.remove(menu_func_export)
    bpy.types.TOPBAR_MT_file_import.remove(menu_func_import)