Fix page DNF System Upgrade headings
    
    Page DNF System Upgrade had incorrect looking headers.
    Top level section "Optional post-ugrade tasks" had only one sub-section,
    "Update system configuration files".
    The next top level section "Upgraded package configurations"
    seemingly continue with the exact same topic,
    and had multiple sub-sections that seemed to fit better under
    "Optional post-upgrade tasks".
    Fixed by simply removing the header "Upgraded package configurations",
    after that everything seems much better.