def delete(record)
      case record
      when ControlPoint
        delete_child(:control_points, record)
      when ExtendedField
        delete_extended_field
      else
        logger.warn("Unknown class (record) given to Field#delete: #{record.class}")
      end
    end
def delete(record)
      case record
      when ControlPoint
        delete_child(:control_points, record)
      when ExtendedField
        delete_extended_field
      else
        logger.warn("Unknown class (record) given to Field#delete: #{record.class}")
      end
    end
Removes the reference of the given instance from this instance.

 @param [ControlPoint, ExtendedField] record a child record to be removed from this instance