Revert "わざと落としてみる"

This reverts commit f4dd5a8.

Author: melpon

tests/client.py

@@ -416,8 +416,6 @@ def _on_disconnect(self, error_code: SoraSignalingErrorCode, message: str) -> No
         if self._fake_video_thread is not None:
             self._fake_video_thread.join(timeout=10)
 
-        self._sora = None
-
     def _on_ws_close(self, code: int, reason: str) -> None:
         print(f"WebSocket closed: code={code} reason={reason}")
         self._ws_close = True