Remove Herald rule edit log

Summary:
Fixes T7601. Ref T7803, weakly (this removes a Query subclass with ad-hoc paging). Herald has a very old edit log which predates transactions and is essentially useless and not really policy-aware. I think it's doing more harm than good; remove it.

Herald rules have proper transactions, but rule edits don't currently render something nice into the transaction log. This is definitely the way forward, but we haven't seen requests for this so don't bother building it for now.

I did put a nice end-cap on the transaction log, though.

Test Plan:

• Viewed Herald UI.
• Grepped for removed classes and methods.
• Edited a rule.
• Viewed rule transaction log.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: cburroughs, chad, epriestley

Maniphest Tasks: T7601, T7803

Differential Revision: https://secure.phabricator.com/D12346