Remove old paged forms

Summary:
Ref T11326. This gets rid of the old multi-paged form stuff used in the last version of Diffusion.

This incidentally removes a callsite for a date control to make it a little easier to simplify them.

Test Plan: Grepped for all removed classes, no more callsites.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11326

Differential Revision: https://secure.phabricator.com/D16302