Voctomix doesn't need a separate loopy source

If do keep loopy in voctomix, it doesn't need to be a separate source, according to https://github.com/voc/voctomix/issues/384 We could just feed it straight into the blanker.

This could significantly simplify our voctomix config. (Assuming we're even able to use loopy, given https://github.com/voc/voctomix/issues/381 )