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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def remove_reserved_binding(vlan_id, switch_ip, instance_id, port_id):
 """Removes reserved binding. This overloads port bindings to support reserved Switch binding used to maintain the state of a switch so it can be viewed by all other neutron processes. There's also the case of a reserved port binding to keep switch information on a given interface. The values of these arguments is as follows: :param vlan_id: 0 :param switch_ip: ip address of the switch :param instance_id: fixed string RESERVED_NEXUS_SWITCH_DEVICE_ID_R1 :param port_id: switch-state of ACTIVE, RESTORE_S1, RESTORE_S2, INACTIVE : port-expected port_id """

    if not port_id:
        LOG.warning("remove_reserved_binding called with no state")
        return
    LOG.debug("remove_reserved_binding called")
    session = bc.get_writer_session()
    binding = _lookup_one_nexus_binding(session=session,
                                        vlan_id=vlan_id,
                                        switch_ip=switch_ip,
                                        instance_id=instance_id,
                                        port_id=port_id)
    for bind in binding:
        session.delete(bind)
    session.flush()
    return binding