Use getPhobjectClassConstant() to access class constants
Summary: Ref T9494. Depends on D14216. Remove 10 copies of this code.
Test Plan: Ran arc unit --everything, browsed Config > Modules, clicked around Herald / etc.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T9494
Differential Revision: https://secure.phabricator.com/D14217