pylint: Clean up __convert_to_gssapi_replication
    
    __convert_to_gssapi_replication has been added in a0bfbec19 and
    then removed in ce2bb47cc without clean up.
    
    Found by Pylint:
    ```
    ipaserver/install/krbinstance.py:589: [W0238(unused-private-member),
    KrbInstance.__convert_to_gssapi_replication] Unused private member
    `KrbInstance.__convert_to_gssapi_replication(self)`)
    ```
    
    Fixes: https://pagure.io/freeipa/issue/9117
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>