Prune unused code from PhabricatorPayloadAnalyzer

Summary:
Some code from GitHubPayloadAnalyzer has been left in this file
in rNOTIFc3f751a0. It's now removed.

Test Plan: Replay back a previous Phabricator payload

Reviewers: dereckson

Differential Revision: http://devcentral.nasqueron.org/D128