Remove user-independent date and time functions from Phabricator
Summary: These have been moved into libphutil.
Test Plan: Browsed Phabricator, didn't see a crash.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D9907