R1:94b96ae53319

Fix visibility of the `PhabricatorWorker::doWork()` methods

Summary: Ref T6822. This method is only called from within the `PhabricatorWorker::executeTask()` and `PhabricatorWorker::scheduleTask()` methods.

Test Plan: `grep`ped for `->doWork`.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6822

Differential Revision: https://secure.phabricator.com/D11406