function rollbackFileSave(db, step, task) {
  var gfs = new Grid(db);

  return dbUtils.removeFile(step.dataStore[0]._id, gfs)
    .then(function () {
      return updateState(task, step.index, ROLLED);
    });
}
Rollback for file save step.

@param db native db
@param step the file save step
@param task the task containing the step.

@returns {Promise|*}