Move `getPEP8WithTextOptions` method into `ComprehensiveLintEngine` class.

Summary: Since this method is only used within this class, it makes sense to move it here.

Test Plan: N/A

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9114