Remove reentrant code
Remove reentrant code

Summary: Ref T7604. Remove the `reenter_if_this_is_arcanist_or_libphutil` function. Some discussion in D12945.

Test Plan: Ran `./bin/arc --trace help` and saw things happen as expected.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7604

Differential Revision: https://secure.phabricator.com/D12999

julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist