refactor(matrix.nix): remove unused PostgreSQL configuration

- Removed the commented-out and unused `postgresql` service configuration from `matrix.nix`.

hosts/architect/matrix.nix

@@ -38,15 +38,6 @@ in
       };
     };
 
-    postgresql = {
-      enable = true;
-      package = pkgs.postgresql;
-      # ensureUsers = [{
-      #   name = db_name;
-      #   ensurePermissions = { "DATABASE \"${db_name}\"" = "ALL PRIVILEGES"; };
-      # }];
-    };
-
     nginx.virtualHosts = {
       # server
       ${domain} = {