Not knowing how your WSUS server is set up, I can't be sure. If no one will need SQL Server 2008 updates then you can decline this update in WSUS and it won't push out to anyone and won't show as failed in any reports.
Best bet would be to hide the update on this machine only then....or just ignore the failing update...or uninstall and strip out all SQL Server stuff and re-install. Let me know what you decide.