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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 unregister(name, server_url):
    '''
    Unregister specified server from Spacewalk

    CLI Example:

    .. code-block:: bash

        salt-run spacewalk.unregister my-test-vm spacewalk01.domain.com
    '''

    try:
        client, key = _get_session(server_url)
    except Exception as exc:
        err_msg = 'Exception raised when connecting to spacewalk server ({0}): {1}'.format(server_url, exc)
        log.error(err_msg)
        return {name: err_msg}

    systems_list = client.system.getId(key, name)

    if systems_list:
        for system in systems_list:
            out = client.system.deleteSystem(key, system['id'])
            if out == 1:
                return {name: 'Successfully unregistered from {0}'.format(server_url)}
            else:
                return {name: 'Failed to unregister from {0}'.format(server_url)}
    else:
        return {name: 'System does not exist in spacewalk server ({0})'.format(server_url)}