Remove derelict openDesktop.org / Attica integrations from about dialog

Old lists of people, abandoned accounts, UI bugs etc. Would need work to get compile on Qt6, doesn't seem worth the effort. Less is more, also removes the dependency on Attica (skimming through lxr.kde.org, Amarok seems to be the only user of some of the Attica functionalities)

The integration fetches the avatars (though their display is broken at the moment) and some extra links to those contributors who have listed them (but very few have, actually, and there's quite a bit of code parsing such properties that are not used by any of the accounts listed)

I guess this is something where I'd be very happy to hear any comments (against or for)

Before: The clickable label that fetches ocs data (corresponding experience also on credits and donors tabs):

Before: The state after clicked to fetch data:

After (the label + relevant backend code stripped away)