ipa-join: extract unenrollment code common to JSON and XML-RPC to separate function
Also fix some some memleaks on the way.
Related: https://pagure.io/freeipa/issue/7966
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>