Unregisters the logging handler.

        :param handler:  A handler previously registered with this loggger.
        :param shutdown: Flag to shutdown the handler.

def _unregisterHandler(self, handler, shutdown=True):
        """
        Unregisters the logging handler.

        :param handler:  A handler previously registered with this loggger.
        :param shutdown: Flag to shutdown the handler.
        """
        if handler in self._handlers:
            self._handlers.remove(handler)
            self._logger.removeHandler(handler)
            if shutdown:
                try:
                    handler.close()
                except KeyError:
                    # Depending on the Python version, it's possible for this call
                    # to fail most likely because some logging module objects get
                    # garbage collected before the VSGLogger object is.
                    pass