Remove leftover proxy change request

These are now handled within the `proxy_with_retry` helper.

mautrix_instagram/user.py

@@ -503,7 +503,6 @@ class User(DBUser, BaseUser):
                 self.start_listen()
         finally:
             self._is_refreshing = False
-            self.proxy_handler.update_proxy_url()
 
     async def _handle_checkpoint(
         self,