__remove_lightweight_ca_key_retrieval_custodia has been added in
8700101d9, but it was never used.
Caught by Pylint:
```
ipaserver/install/cainstance.py:1308: [W0238(unused-private-member),
CAInstance.__remove_lightweight_ca_key_retrieval_custodia]
Unused private member
`CAInstance.__remove_lightweight_ca_key_retrieval_custodia(self)`)
```
Fixes: https://pagure.io/freeipa/issue/9117
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>