delete images that have been unattached from properties (as they are no longer in the import file)

gistfile1.txt

add_filter('wp_all_import_is_post_to_update', 'wpai_wp_all_import_is_post_to_update', 10, 5);
function wpai_wp_all_import_is_post_to_update($continueImport, $pid, $currentXmlNode, $importID, $simpleXml) {
	$images = get_attached_media( 'image', $pid );
	$ids = [];
	foreach ($images as $image) {
		$ids[] = $image->ID;
	}
	update_option('_wpai_attached_images_before_import_' . $pid, $ids);
	return $continueImport;
}

add_filter('pmxi_saved_post', 'wpai_pmxi_saved_post', 10, 3);
function wpai_pmxi_saved_post($pid, $rootNodes, $isUpdate) {
	$attached_images_before_import = get_option('_wpai_attached_images_before_import_' . $pid);
	if (!empty($attached_images_before_import)) {
		$images = get_attached_media( 'image', $pid );
		$ids = [];
		foreach ($images as $image) {
			$ids[] = $image->ID;
		}
		$missing = array_diff($attached_images_before_import, $ids);
		foreach ($missing as $image) {
			wp_delete_attachment( $image ); 	
		}
	}
}