Removed unused loadGitLocalRefs() from PhabricatorRepositoryPullEngine

Summary:
rP2b0ad243d179f81baad24ccd9748a4ba59017d25 introduced private function loadGitLocalRefs().
In rPe910c76e65e54a439a0af4735ae89c70076673d5, the only call to loadGitLocalRefs() was removed, using loadGitRemoteRefs() to load (and compare) both remote and local refs. Thus remove this unused method.

Test Plan: Read/grep the code in PhabricatorRepositoryPullEngine.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25718