code: def remove_session_ref(self, session_id: str):
      del self._session_refs[session_id]
  
imports: import asyncio
  import functools
  import logging
  import os
  import time
  from typing import Dict, List, Optional
  from ....None import oscar
  from ....utils import to_binary
  from ...cluster import ClusterAPI
  from ...core import NodeRole, create_service_session, destroy_service_session
  from ..core import SessionInfo
label_desc: Use image node_id 5 for calling the SessionManagerActor obj's underlying member method code with example usage: obj.remove_session_ref(session_id) without return types