add_filter('wcfm_shipment_tracking_fields', function($fields) {
    if( isset( $fields['wcfm_tracking_code'] ) ) {
        unset( $fields['wcfm_tracking_code']['custom_attributes'] );
    }
    if( isset( $fields['wcfm_tracking_url'] ) ) {
        unset( $fields['wcfm_tracking_url']['custom_attributes'] );
    }

    return $fields;
});