Variable to config: system.date [d7]

  update_variables_to_config('system.date', array(
    'site_default_country' => 'country.default',
    'date_first_day' => 'first_day',
    'date_default_timezone' => 'timezone.default',
    'configurable_timezones' => 'timezone.user.configurable',
    'empty_timezone_message' => 'timezone.user.warn',
    'user_default_timezone' => 'timezone.user.default',
  ));

See parent issue #2181257: [meta] Variables to config migration [d7] for instructions.