UCS 5.0 upgrade failed: solve pre-update check python-ucr-template-compatibility

During the upgrade to UCS 5.0 all UCR templates are checked to contain Python 3 compatible syntax.
If templates are detected which are not compatible, the upgrade is blocked.

Each template has to be checked individually for possible solutions.
In general either the template may be removed as it is part of an old/uninstalled but not-purged package or the template belongs to an App, which is not yet released for UCS 5.0 and which needs an upgrade.

python_ucr_template_compatibility:
The following UCR templates are not compatible with Python 3:

/etc/univention/templates/files/var/www/ucs-overview/en.html.d/01en.html (package: univention-apache)
/etc/univention/templates/files/var/www/ucs-overview/en.html.d/99en.html (package: univention-apache)
/etc/univention/templates/files/var/www/ucs-overview/de.html.d/01de.html (package: univention-apache)
/etc/univention/templates/files/var/www/ucs-overview/de.html.d/99de.html (package: univention-apache)
/etc/univention/templates/files/etc/security/netfilter.d/20time (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20dns (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20http (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20ftp (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20ipp (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20imap (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20tftp (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20https (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20smtp (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20dhcp (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20nagios (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20notifier (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20sieve (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20krsh (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20x11 (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20samba (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/17localhost (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20nfs (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20postgres (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20umc (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20ssh (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20kerberos (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20ldap (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20pop3 (package: univention-firewall)
/etc/univention/templates/files/etc/security/netfilter.d/20telnet (package: univention-firewall)
/etc/univention/templates/files/etc/cups/cupsd.conf (package: univention-printserver)
/etc/univention/templates/files/etc/cups/cups-access-limit.conf (package: univention-printserver)
/etc/univention/templates/files/etc/postgresql/9.1/main/pg_hba.conf.d/10-appcenter
/etc/univention/templates/files/var/www/ucs-overview/entries.json
/etc/univention/templates/files/usr/share/univention-management-console-frontend/entries.json

→ These templates are configuration files, which weren’t correctly cleaned up during package upgrade. They can be removed safely.

If you find files not listed here please report them in a new forum thread.