spec: Drop no longer used build dependency on paste
    
    With ff6e701b0077d9c8e2aacdcaecf70f885018db92 it was replaced
    with `werkzeug`.
    
    https://pypi.org/project/Paste/
    > Paste is in maintenance mode and recently moved from bitbucket to
      github. Patches are accepted to keep it on life support, but for the
      most part, please consider using other options.
    
    Fixes: https://pagure.io/freeipa/issue/9314
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>