Deprecate https://coli-conc.gbv.de/rvk/api/

[nichtich]

Looks like the main JSKOS server instance at https://coli-conc.gbv.de/api/ can handle RVK as well. Better not have two versions of the same data.

[stefandesu]

Data in the main instance should be updated before making the switch. Before doing that, it would make sense to update https://github.com/gbv/jskos-data/tree/master/rvk to the latest data (2024_4).