I was using OSLC to update the ValidatedBy attribute in DNG, but, I do not find any methodology to delete the already existing test links in the ValidatedBy field against any artifact.
Check out section 6 (or look for "remove a link") in the below article and let us know whether you are able to do it.
https://jazz.net/library/article/1197
Dashboards and work items are no longer publicly available, so some links may be invalid. We now provide similar information through other means.
Learn more here.