Some parts are blurred:
Deleting links to bugs (or anything else) from a Test Execution is currently not possible.
You may open a feature request on GitHub Issues to request this functionality.
However these URLs serve the purpose of traceability b/w your bug reports & test executions. If the link is removed that breaks traceability. You'd better have a very good justification for that because it doesn't sound like something a test team would like to do.