The use of bare username/password combos to do API calls has been
dropped by GitHub, as of 2020-11-13:
https://developer.github.com/changes/2020-02-14-deprecating-oauth-auth-endpoint/
Let's switch to expecting a token in the rake jobs that update the book
and manpage content. The PAT can be very limited, as it only needs to
access public repos (the only reason we need to auth at all is to
overcome API rate limiting).
Once upon a time, the idea was that you could update the
site with new book versions by posting to a special endpoint
with a secret token.
But these days we fetch the book material directly to the
rails environment by running a periodic rake task, and then
update the database directly. Let's drop this unused code.