class_docstr: CertStore represents a persistent file-based record of certificates, each associated with a
  particular master url.
code: def delete_cert(self, url: str) -> None:
      with self._persistent_store() as store:
          if url in store:
              del store[url]
  
imports: import atexit
  import contextlib
  import json
  import logging
  import os
  import pathlib
  import tempfile
  from typing import Dict, Iterator, Optional, Union, cast
  import certifi
  import filelock
  from determined.common import api, util
label_desc: Use image node_id 6 for calling the CertStore obj's underlying member method code with example usage: obj.delete_cert(url) without return types