Remove configuration for repository housekeeping and/or bitmaps

The following discussion from !20863 (merged) should be addressed:

• @nick.thomas started a discussion: (+4 comments)

  I don't have data on how expensive the :gc call is. Running it locally on the post-move gitlab-foss repository, it completed in under a minute, so I'm not very worried. I do think we'll want to test it in production though, hence the feature flag.

  Instead of, or perhaps in addition to, the FF, is the possibility of respecting Gitlab::CurrentSettings.housekeeping_enabled?. I've left it out for now, but I can see an argument that we should pay attention to it here. Thoughts?

Right now, we allow repository housekeeping to be disabled entirely, and we have similar configuration for git bitmaps. I'd like to suggest that we remove these configuration options.

The justification is that housekeeping tasks, and particularly bitmap creation, has a significant performance impact (e.g. gitaly#2108 (closed) ). Making gitlab performant under both configurations is much more work than making it performant under a single condition.