remove dead modules/retiolum.nix

This was an old copy of the krebs retiolum module with NIX_PATH lookups
(<retiolum/hosts>, <system-secrets/...>). It was never imported — the
upstream retiolum.nixosModules.retiolum from the flake input is used
instead (in profiles.default), with configs/retiolum.nix overriding
the key paths to agenix secrets.

modules/retiolum.nix

@@ -1,73 +0,0 @@
-{
-  config,
-  pkgs,
-  lib,
-  ...
-}:
-with lib;
-let
-  netname = "retiolum";
-  cfg = config.networking.retiolum;
-in
-{
-  options = {
-    networking.retiolum.ipv4 = mkOption {
-      type = types.str;
-      description = ''
-        own ipv4 address
-      '';
-    };
-    networking.retiolum.ipv6 = mkOption {
-      type = types.str;
-      description = ''
-        own ipv6 address
-      '';
-    };
-    networking.retiolum.nodename = mkOption {
-      type = types.str;
-      default = config.networking.hostName;
-      description = ''
-        tinc network name
-      '';
-    };
-  };
-
-  config = {
-    services.tinc.networks.${netname} = {
-      name = cfg.nodename;
-      hosts = builtins.mapAttrs (name: _: builtins.readFile "${<retiolum/hosts>}/${name}") (
-        builtins.readDir <retiolum/hosts>
-      );
-      rsaPrivateKeyFile = toString <system-secrets/retiolum.key>;
-      ed25519PrivateKeyFile = toString <system-secrets/retiolum.ed25519>;
-      extraConfig = ''
-        LocalDiscovery = yes
-        AutoConnect = yes
-      '';
-    };
-
-    networking.extraHosts = builtins.readFile (toString <retiolum/etc.hosts>);
-
-    environment.systemPackages = [ config.services.tinc.networks.${netname}.package ];
-
-    networking.firewall = {
-      allowedTCPPorts = [ 655 ];
-      allowedUDPPorts = [ 655 ];
-    };
-    #services.netdata.portcheck.checks.tinc.port = 655;
-
-    systemd.network = {
-      enable = true;
-      networks = {
-        "${netname}".extraConfig = ''
-          [Match]
-          Name = tinc.${netname}
-
-          [Network]
-          Address=${cfg.ipv4}/12
-          Address=${cfg.ipv6}/16
-        '';
-      };
-    };
-  };
-}