Change MAY to SHOULD for fedora-obsolete-packages inclusion
    
    The logic that we use in Fedora has changed: in the past we were perfectly happy
    with users having to do various magical incantations during upgrades. Nowadays
    we expect upgrades to go smoothly. If a package causes a "dependency issues
    which interfere[s] with upgrades or [is] otherwise harmful" we expect the package
    to be removed, period. Thus, the recommendation is changed to SHOULD.
    
    (I would go for "MUST", because *somebody* will have to do this, it's not clear
    *who*. Sometimes it'll be the person retiring the package, but most often it'll
    just be somebody who notices that the upgrade path is broken. Those events are
    often separated in time. Also, we can't/don't want to block package retirement.
    So it's "a packager SHOULD", not "the package MUST".)
    
    Also change the section title, because people might be looking how to obsolete
    a package, but the title suggested that the section is about renames only.