Update stale comment for unlinking repos
Previous to commit c02b9ad1 (UnlinkRepositoryFromObjectPool: stop removing objects/info/alternates, 2019-03-29), we removed the "objects/info/alternates" file for a repository when unlinking it from its object pool. While the commit changed it to not delete the file anymore, it forgot to update a comment that claims we still do.
Update the comment to avoid confusion.
Edited by 🤖 GitLab Bot 🤖