Remove the friggin' demos entirely or at least mostly

Background

• The demos, generally, generate a disproportionate amount of support burden, in multiple "why doesn't this copypasta work?" and "hey the demo is actually broken in XYZ ways" flavors.
• Furthermore, a large proportion of them really boil down (to me) as "ugh why aren't you just using Fabric (2) for this, it's basically the real world reference implementation".

TODO

• Identify exactly which demos are covered by Fabric, which aren't but should/can be, and which are truly extra use cases that don't deserve their own high level implementation
• If that leaves us with no demos, great, remove the entire folder, and make sure we link to Fabric 2 explicitly in the README and docs.
• Otherwise:
  • Remove the first category entirely, and put a README in the demos folder repeating the plea to use Fabric 2.
  • If there are any in the 2nd category, make Fabric tickets for 'em, and remove 'em.
  • If there's anything left in the 3rd category for some reason, leave them as-is.

Start by inventorying the demos folder and comparing each demo with Fabric 2 to classify what should be removed, migrated, or retained. Review the README and docs references before making any removals. Done means the demo set follows the classification, Fabric 2 is linked explicitly, and any needed Fabric tickets are recorded.