Summary:
Ref T13098. Makes some tests pass by updating `'phutil'` to `'arcanist'`. Skips some tests which won't pass for a while.
Also removes external test engines for now since they aren't realistically going to run for a while and they significantly complicate bootstrapping a set of passing tests out of `arc unit`.
Test Plan: Ran `arc unit`, saw fewer failures.
Reviewers: amckinley
Reviewed By: amckinley
Subscribers: aurelijus
Maniphest Tasks: T13098
Differential Revision: https://secure.phabricator.com/D19714
