refactor(nixos): derive RomM nginx host from route

configs/nixos/guests/romm.nix

@@ -131,9 +131,9 @@ in
         ];
 
     guests.romm = {
-      interior.modules.services.romm = {
-        enable = true;
-        virtualHost = cfg.reverseProxy.route.domain;
+      interior = {
+        modules.services.romm.enable = true;
+        services.romm.nginx.virtualHost = cfg.reverseProxy.route.domain;
       };
 
       mounts = {

configs/nixos/modules/services/romm.nix

@@ -16,12 +16,6 @@ in
       readOnly = true;
       description = "Path to RomM's environment file.";
     };
-
-    virtualHost = lib.mkOption {
-      type = lib.types.str;
-      example = "romm.example.org";
-      description = "Public host name configured in RomM's nginx.";
-    };
   };
 
   config = lib.mkMerge [
@@ -41,7 +35,6 @@ in
         database.createLocally = true;
         redis.createLocally = true;
         watcher.enable = true;
-        nginx.virtualHost = cfg.virtualHost;
         inherit (cfg) environmentFile;
       };