Stop threading handles through the CustomField + ApplicationSearch pipeline

Summary:
Ref T8441. Ref T7715.

• These are obsolete after the Viewer/HandlePool changes.
• These are unused after the typeahead parameterization changes.

Test Plan: grep, poked around.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7715, T8441

Differential Revision: https://secure.phabricator.com/D13176