refactor: split out game engine experiment and demo game

scripts/install_apps.sh

@@ -41,7 +41,6 @@ APPS=(
     "charmap|apps/scalable/accessories-character-map.svg"
     "printers|devices/scalable/preferences-devices-printer.svg"
     "timezone|categories/scalable/preferences-system-time.svg"
-    "rpgdemo|apps/scalable/utilities-terminal.svg"
     "paint|apps/scalable/kolourpaint.svg"
     "screenshot|apps/scalable/gnome-screenshot.svg"
     "texteditor|apps/scalable/accessories-text-editor.svg"