Fold ArcanistPhutilXHPASTLinter into ArcanistXHPASTLinter
Summary: I've been thinking about this for a while... why not just fold ArcanistPhutilXHPASTLinter into ArcanistXHPASTLinter?
Test Plan: arc unit
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D13867