R1:5c1e4488deda

Remove all "Phabricator Bot" code

Summary:
Closes T7829 as wontfix. Closes T7965 as wontfix. Closes T7800 as wontfix. Closes T2731 as wontfix. Closes T1271 as wontfix.

We aren't maintaining this at all (see, e.g., T7829) and a user reported a technically accurate security issue via HackerOne: <https://hackerone.com/reports/222870>

Just throw it away until we get to the eventual Conphernece bot/API update and can do this stuff correctly.

Test Plan: Grepped for `phabricatorbot`.

Reviewers: chad…