pylint: Fix unused-private-member
Pylint 2.9.0 introduced new checker:
> Emitted when a private member of a class is defined but not used
Fixes: https://pagure.io/freeipa/issue/9117
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>