Fails to migrate to amber-phone due to missing dependency

See https://master.pureos.net/migrations/excuse/f36bd79c-4dc1-487b-ad57-6d5d1bb457af

it depends on librust-xcb-0.8+default-dev and librust-xcb-0.8+xkb-dev which in fact i can't find anywhere. squeekboard itself migrated so it's not super important but should be fixed since it will cause trouble when we e.g. need to do a targeted rebuild agains amber-phone. possible fix would be to just drop the x11 related packages since we don't use them.