Make some confusing/weird Calendar fields not configurable on custom EditEngine forms

Summary:
Ref T11816.

• Host gets weird behavior around defaulting to the viewer.
• Invitees get weird behavior around defaulting to the viewer.
• "All Day" is just sort of weird since start / end date aren't customizable.
• Recurring/Frequency are weird here and don't make much sense.

I can't immediately come up with reasons that any of these are particularly useful/valuable to default. More of them can be made editable after T10222 gets sorted out.

Test Plan: Edited edit engine custom forms for Calendar events, saw a more sensible list of customizable fields (e.g., policy stuff).

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11816

Differential Revision: https://secure.phabricator.com/D16878