phabricator_format_timestamp => phabricator_datetime

Summary: make the change, kill the function. be sure to get a good $user or
$viewer variable

Test Plan:
for each controller or view, look at it in the ui. change timezone, refresh ui
and note change. i did not test the OAuthSettingsPanelController; not sure how
to get to that badboy and i got a bit lazy

Maniphest Tasks: T222

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, btrahan, epriestley

Maniphest Tasks: T222

Differential Revision: 1166