docs: def get_parents():
      """Return sorted list of names of packages without dependants."""
      distributions = get_installed_distributions(user_only=ENABLE_USER_SITE)
      remaining = {d.project_name.lower() for d in distributions}
      requirements = {r.project_name.lower() for d in distributions for
                      r in d.requires()}
  
      return get_realnames(remaining - requirements)