git/housekeeping: Always enable writing cruft packs

In e4a9ded8 (housekeeping: Wire up logic to conditionally generate cruft packs, 2023-03-03), we have wired up the logic to generate cruft packs during repository housekeeping. Cruft packs are a rather recent addition to Git: instead of keeping unreachable objects as loose objects until they expire and get pruned, they are instead tracked in a separate packfile. This both reduces the overhead of having to store the loose objects as Git can make use of improved compression, and it speeds up access times for objects as Git does not have to search through so many loose objects anymore.

We have since rolled out this new feature to production successfully. So let's remove the feature flag and thus unconditionally enable writing cruft packs.

Closes #4829 (closed).