Mark a device as non exported in database

        :param argin: Device name
        :type: tango.DevString
        :return:
        :rtype: tango.DevVoid

def DbUnExportDevice(self, argin):
        """ Mark a device as non exported in database

        :param argin: Device name
        :type: tango.DevString
        :return:
        :rtype: tango.DevVoid """
        self._log.debug("In DbUnExportDevice()")
        dev_name = argin[0].lower()
        self.db.unexport_device(dev_name)