Remove some unused Releeph field methods

Summary: Ref T3718. Remove `bulkLoad()` and header-view rendering wrappers.

Test Plan: Viewed a request, looked the same. `grep`'d for stuff.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T3718

Differential Revision: https://secure.phabricator.com/D8809