Remove arcconfig settings from ArcanistLinterTestCase

Summary: This doesn't make too much sense anymore as all modern linters are configured via the .arclint file rather than .arcconfig.

Test Plan: grepped to make sure this option isn't used.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11173