try to fix ipykernel

Author: blink1073

jupyter_client/threaded.py

@@ -243,9 +243,6 @@ def stop(self) -> None:
         self.close()
         self.ioloop = None
 
-    def __del__(self):
-        self.close()
-
     def close(self) -> None:
         if self.ioloop is not None:
             try: