Fix R-rgdal comment
    
    This fixes the comment to say that R-rgdal obsoletes can be dropped in
    F41, not in F43.
    
    R-rgdal was retired in F39, and was not part of the F39 release package
    set. This means that in order to support distro upgrades across 2
    releases, we'll need to have the obsoletes in place for F38->F39, and
    F38->F40 upgrades.  After that, for F41, the obsoletes can be dropped.