2wkatomic: Generate a delta from the previous stable
    
     - Requires the repos be merged
     - Stop doing release substitution in the ref, since it changed for 26+
    
    Resolves: https://pagure.io/releng/issue/6871
    
    (Note, not tested)
    
    Signed-off-by: Colin Walters <walters@verbum.org>