Ref T13098. Continue to chip away at unit tests.

I stubbed out the read of configuration directly from RepositoryAPI and would like to remove it later. This is the only configuration value that RepositoryAPI reads directly. Instead, I suspect this will be cleaner if higher-level callers are responsible for reading and applying commit range rules and the actual RepositorAPI object does not know about them.

(In this particular case it's pretty moot anyway since unit tests shouldn't depend on .arcconfig settings.)

Ran unit tests, got slightly fewer failures.