Remove XB demo

Closes #3501987

.ddev/config.yaml

@@ -26,8 +26,6 @@ hooks:
     # see the warning about Node.js Snap for Linux at
     # https://docs.cypress.io/guides/getting-started/installing-cypress.
     - exec: 'test -d node_modules || npm clean-install --foreground-scripts'
-    # Build Experience Builder's JavaScript bundle, if needed.
-    - exec: 'XB_UI_PATH=$DDEV_DOCROOT/modules/contrib/experience_builder/ui; test -d $XB_UI_PATH/dist || ( npm --prefix $XB_UI_PATH install && npm --prefix $XB_UI_PATH run build )'
 web_environment:
   # If CANARY is set, Composer will install dev branches of all dependencies (be sure to
   # run `ddev rebuild` if you change this).