access_checks: Always enable use of quarantine directory
What does this MR do and why?
Remove the feature flag that guards the use of the quarantine directory when enumerating new commits for access checks. With this feature flag gone, enumerating new commits is going to be a lot faster in repos with many references given that we don't have to walk the repository's object graph anymore, but instead only have to take a peek into the quarantine directory that contains all new objects.
With the feature flag gone, there are no callers of #new_commits
anymore which disable use of the quarantine directory. So let's also
drop that parameter while at it.
Closes #361174 (closed)