refactor: 移除没用的return

Author: shuiping233

astrbot/core/platform/sources/kook/kook_client.py

@@ -422,8 +422,6 @@ async def upload_asset(self, file_url: str | None) -> str:
         except Exception as e:
             raise RuntimeError(f"上传文件到kook服务器异常: {e}") from e
 
-        return ""
-
     async def wait_until_closed(self):
         """提供给外部调用的等待方法"""
         await self._stop_event.wait()