Remove two unused SearchEngine methods

Summary:
Ref T11326. These are last-generation and neither of these have callsites anymore.

(I nuked these since I'm trying to simplify date handling.)

Test Plan: Grepped for callsites.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11326

Differential Revision: https://secure.phabricator.com/D16301