Remove the `xb_dev_standard` module, instead recommend using XB's `test_site` recipe for development

Using these recipes to install XB doesn't invoke the install hook that enables the xb_stark theme, which is evident in the tests for 📌 Provide salient warning when xb_stark not enabled Active . I'd like to be sure this is addressed before (or as part of) removing xb_dev_standard, or we at least do the steps necessary for #3538562 to land. Currently when xb_stark isn't present, it could be seen as any number of triage-burden-amplifying bugs.

Shoot, you're very right 😑 Very grateful for you calling that out! Thanks! 🙏