R1:37f35e9ecca6

Remove "viewerDateFrom" / "viewerDateTo" in favor of CalendarDateTime methods

Summary: Ref T10747. The CalendarDateTime object now carries the viewer timezone as part of its state, so we don't need to have separate accessors.

Test Plan:
- Viewed events, checked that crumbs render properly.
- Edited events.
- Created new events.
- Viewed calendar.
- Viewed event detail pages.
- Viewed profile mini-calendar.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10747

Differential Revision…