Hide time controls when editing all-day Calendar events

Summary:
Ref T11326. When an event is all-day, hide the time controls for the start/end dates. These aren't used and aren't helpful/useful.

This got a little more complicated than it used to be because EditEngine forms may have only some of these controls present.

Test Plan: Edited an all-day event; edited a normal event; swapped an event between normal and all-day.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11326

Differential Revision: https://secure.phabricator.com/D16327