Remove loadPhabricatorRepository from ReleephProject

Summary: Ref T3551. Repository is guaranteed if a product is loaded with modern mechanisms.

Test Plan:
  - Edited a request.
  - Called `releephwork.getbranchcommitmessage`.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T3551

Differential Revision: https://secure.phabricator.com/D8821