Similar like for the white label themes that we offer Open Source Xibo
Xibo CMS is distributed under AGPLv3 licence and that does not change with white label theme or any modifications you make to it.
As such it must satisfy the terms of the AGPLv3 licence, while yes you can edit that page and change/remove those links (as we do with white labels on request and signed document), if you do that then you need to satisfy AGPLv3 licence requirements by other means.
If you’re interested in the white label CMS theme and want to remove those links from the login page, please create support ticket with Spring Signage.