the derivations build successfully again (except for the
universially-broken maps package), but were not yet proven to work with
the nixos module, since a configuration variable for the frontend
package was changed in this update.

This updates all packages, as far as possible. The tcm derivations
appear to be all broken for now, as are the maps packages of both xce
versions (which should not be a problem in deployments which don't use
them, as these should not be evaluated at all).

this is based on the xce-unfederated branch of the workadventure-xce
repository [1], and requires some reworking of the general derivation
code since it currently uses older package sets than the other versions.

[1] https://github.com/workadventure-xce/workadventure-xce/tree/xce-unfederated

updates:
 - workadventure-xce to the latest commit
 - workadventure-tcm to the latest commit

this removes the fediventure-version, as it appears to be no longer
updated, and since the workadventure-xce version now also includes the
relevant patches for the current federation features.

The maintainers of both of these forks are now collaborating on workadventure-xce,
and have apparently both deprecated their own versions in favour of it (see [1]
for hasi; tabascoeye does not explicitely state as much, but has changed their
description to reflect that of the workadventure-xce repository).

[1] https://gitlab.hasi.it/herzi/project/workadventure

This is the version currenlty on the feature/fediventure branch in the
workadventure repository of the fediventure group at

https://gitlab.com/fediventure/workadventure/-/tree/feature/federation