docs: def purge_items(app, env, docname):
      """
      Clean, if existing, ``item`` entries in ``traceability_all_items``
      environment variable, for all the source docs being purged.
  
      This function should be triggered upon ``env-purge-doc`` event.
  
      """
      keys = list(env.traceability_all_items.keys())
      for key in keys:
          if env.traceability_all_items[key]['docname'] == docname:
              del env.traceability_all_items[key]