[Wilds] Make more test cases (mostly related to the phutil -> arcanist move) pass

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