Modernize .arcconfig.

Summary: There have been several changes to the .arcconfig file format since this repository was last updated. In addition, the PhutilLintEngine no longer exists.

Test Plan: Eyeball it.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9445