Remove rendering support for very old Repository transactions
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 URIs, Passphrase credentials, and general modernization.
Test Plan: Grepped for all constants, got no hits.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D19828