German translation: 4 more localized maps

As per Crommy's suggestion, Spellkeep is translated with Bannheim.
Map localization: Remove duplicate old generation overlays

For those languags where new overlays are available, we don't need
to keep the old ones.

In fact, we probably should move even those which aren't replaced yet
to the 'resources' repo as they are unused but are currently distribted
with the game.