Restore PEP8 errors.

Summary: As per the TODO comment, now that `.arclint` is more mature, we should be able to restore PEP8 errors.

Test Plan: N/A

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9473