R1:bfbc0e638ddf

Remove vestigal "tags" stuff from Herald

Summary: Ref T8726. No clue what this was.

Test Plan: Grepped for usage, found none.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: eadler, epriestley

Maniphest Tasks: T8726

Differential Revision: https://secure.phabricator.com/D13498