Removes a slot NIO binding.

        :param slot_number: slot number
        :param port_number: port number

        :returns: removed NIO instance

def slot_remove_nio_binding(self, slot_number, port_number):
        """
        Removes a slot NIO binding.

        :param slot_number: slot number
        :param port_number: port number

        :returns: removed NIO instance
        """

        try:
            adapter = self._slots[slot_number]
        except IndexError:
            raise DynamipsError('Slot {slot_number} does not exist on router "{name}"'.format(name=self._name,
                                                                                              slot_number=slot_number))

        if adapter is None:
            raise DynamipsError("Adapter is missing in slot {slot_number}".format(slot_number=slot_number))

        if not adapter.port_exists(port_number):
            raise DynamipsError("Port {port_number} does not exist in adapter {adapter}".format(adapter=adapter,
                                                                                                port_number=port_number))

        yield from self.slot_disable_nio(slot_number, port_number)
        yield from self._hypervisor.send('vm slot_remove_nio_binding "{name}" {slot_number} {port_number}'.format(name=self._name,
                                                                                                                  slot_number=slot_number,
                                                                                                                  port_number=port_number))

        nio = adapter.get_nio(port_number)
        if nio is None:
            return
        yield from nio.close()
        adapter.remove_nio(port_number)

        log.info('Router "{name}" [{id}]: NIO {nio_name} removed from port {slot_number}/{port_number}'.format(name=self._name,
                                                                                                               id=self._id,
                                                                                                               nio_name=nio.name,
                                                                                                               slot_number=slot_number,
                                                                                                               port_number=port_number))

        return nio