3791523 Fix many `link-checker.sh` warnings and errors

Authored and Committed by oturpe 7 months ago
    Fix many `link-checker.sh` warnings and errors
    
    The most common warning is about redirects. Such links are replaced
    with direct links. In some cases better syntax for the same URL is
    used, and in a single case the link target seems to be completely gone,
    so the link is just removed.