abort experiment if no urls returned

internal/engine/inputloader.go

@@ -360,14 +360,10 @@ func (il *InputLoader) loadRemoteOpenVPN(ctx context.Context) ([]model.OOAPIURLI
 	}
 
 	if len(urls) <= 0 {
-		// loadRemote returns ErrNoURLsReturned at this point for webconnectivity,
-		// but for OpenVPN we want to return a sensible default to be
-		// able to probe some endpoints even in very restrictive environments.
-		// Do note this means that you have to provide valid credentials
-		// by some other means.
-		for _, endpoint := range openvpn.DefaultEndpoints {
-			urls = append(urls, model.OOAPIURLInfo{URL: endpoint.AsInputURI()})
-		}
+		// At some point we might want to return [openvpn.DefaultEndpoints],
+		// but for now we're assuming that no targets means we've disabled
+		// the experiment on the backend.
+		return nil, ErrNoURLsReturned
 	}
 	return urls, nil
 }