Remove `clean_updates` entirely, it's no longer needed
    
    Summary:
    `clean_updates` was added to cope with updates being deleted
    from Bodhi. With Bodhi 2, this is expressly disallowed, updates
    cannot be deleted. So we really don't need `clean_updates` at
    all any more.
    
    Test Plan:
    I guess check everything still works, no reason why
    it shouldn't. If you want to satisfy yourself that deleting
    updates is no longer possible in Bodhi 2, see e.g.
    https://github.com/fedora-infra/python-fedora/blob/develop/fedora/client/bodhi.py#L181-L186
    
    Reviewers: tflink, mkrizek
    
    Reviewed By: mkrizek
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D1051