R1:03f249baf349

Remove rendering support for very old Repository transactions

Summary:
Depends on D19827. Ref T13221. Ref T13216. To prepare Repositories for a move to ModularTransactions, throw away some very old transaction rendering code.

This will cause these very old transactions (none of which have been written since at least April 2016) to render "epriestley edited this repository." instead of "epriestley changed the SSH login for this repository from X to Y."

These edits were generally obsoleted by repository…