Remove unused shouldUse* functions from PhabricatorRepository

Summary:
Calls to private functions PhabricatorRepository::shouldUseSSH() and PhabricatorRepository::shouldUseHTTP() were removed in https://we.phorge.it/rP29d1115037b84454c4fd186c47f33f162cc337b9.
Call to private function PhabricatorRepository::shouldUseSVNProtocol() was removed in https://we.phorge.it/rP575c01373ee77c12b06696b34cfdf43a2eb26c42.

Test Plan: Grep the code; run static code analysis.

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/D25786