When destroying an object, destroy its Herald transcripts too

Summary: Ref T5915. Make `bin/remove destroy` a bit more thorough, since Herald transcripts can have field information in them.

Test Plan: Used `bin/remove destroy` to nuke revisions, saw their transcripts vanish too.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5915

Differential Revision: https://secure.phabricator.com/D10306