R1:5b38d2142c06

Remove the dashboard "template" workflow

Summary:
Depends on D20364. Ref T13272. When you create a dashboard, we currently give you a modal choice between an empty dashboard and a "simple template" dashboard.

Remove this choice, and create an empty dashboard in all cases instead.

I think this template dashboard flow isn't terribly useful, and is partly covering over other deficiencies in the workflow. I'm fixing many of those and suspect we can get away without this now. Users on this flow also may not…