Remove the trigger for the first-login mode

It wasn't really ever well-integrated to the system. It was sort
of a kludge hack to spawn it here, and simply skip some pages.

We're not removing the architecture behind the existing-user mode,
as we might very well re-add a better-integrated mode later which
skips some of these pages, but just keep it from spawning for now.
Clean up various TODOs/READMEs, etc.