clan: migrate internal DNS to coredns service

Currently using a patched version of the upstream
coredns service, with hard-coded IPs until
wireguard exports are supported.

Zerotier connections were flaky and wireguard
seems more stable (although it seems to have a bit
less throughput).

machines/crocus/configuration.nix

@@ -7,8 +7,6 @@
     ./radicle.nix
     self.nixosModules.nix-defaults
     ../../modules/remote-builder.nix
-    ../../modules/unbound.nix
-    ../../modules/unbound-auth.nix
     self.inputs.srvos.nixosModules.server
     self.inputs.srvos.nixosModules.hardware-hetzner-cloud
   ];