/**
 * Implements hook_field_delete_revision().
 */
function {{ machine_name }}_field_delete_revision($entity_type, $entity, $field, $instance, $langcode, &$items) {
  list($id, $vid, $bundle) = entity_extract_ids($entity_type, $entity);
  foreach ($items as $delta => $item) {
    // For hook_file_references, remember that this file is being deleted.
    $item['file_field_name'] = $field['field_name'];
    if (file_field_delete_file($item, $field, $entity_type, $id)) {
      $items[$delta] = NULL;
    }
  }
}