Restructure flake.nix for a simpler config for building different images off the same NixOS config.

nix/configuration/roles/chromecast/default.nix

@@ -17,15 +17,9 @@
     };
   };
 
-  config = lib.mkIf config.me.chromecast.enable (
-    lib.mkMerge [
-      {
-        environment.systemPackages = with pkgs; [
-          catt
-        ];
-      }
-      (lib.mkIf config.me.graphical {
-      })
-    ]
-  );
+  config = lib.mkIf config.me.chromecast.enable {
+    environment.systemPackages = with pkgs; [
+      catt
+    ];
+  };
 }