If you don’t need OX anymore you should purge the packages:
apt purge univention-ox-dependencies-master univention-ox-directory-integration (make sure ucr get ox/master/42/registered_ldap_acls is set to yes, otherwise don’t purge).
Then see, if purging removes the extended attributes? Otherwise they can be removed manually.
guacamole is not yet ready for UCS 5.0, I guess the vendor is working on it. Please re-check a few weeks later.