Fix Repository Cleanup Keep-arounds

Right now the repository cleanup service sends the commit mapping to gitaly, then simply deletes any diffs/notes on those old commit shas. This means the MR UI likely doesn't display anything after this. If we are okay with this, then we should also remove any keep-arounds on these old commit IDs.

This would solve one major painpoint in gitlab that it is difficult to rewrite history and remove accidentally pushed secrets.