Do not make optional dependencies required
    
    This content of the requirements.txt file is processed in the setup.py
    and added/declared as being what pagure requires to work.
    But, if you deploy pagure, say with openid login, you do not need
    flask-oidc, but if you keep it in the list, it's added to the .egg-info/
    requires file as being required and when something queries pkg_resources
    it will complain that flask-oidc is required and missing and make the
    app crash.
    
    So let's keep optional packages not required :)
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>