Fix the visibility of PhutilDaemon::run methods

Summary: Ref T6822. This method is only called from PhutilDaemon::execute() and can be made protected.

Test Plan: Launched a daemon with ./bin/phd launch.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T6822

Differential Revision: https://secure.phabricator.com/D11404