function _quitAltGrMode() {
        _enabled = true;
        _ctrlDown = CtrlDownStates.NOT_YET_DETECTED;
        _altGrDown = false;
        _lastTimeStamp = null;
        _lastKeyIdentifier = null;
        $(window).off("keyup", _onCtrlUp);
    }
@private
Resets all the flags and removes _onCtrlUp event listener.