layer1: remove old namespace watcher helpers

pkg/buildermgr/ns_watcher.go

@@ -101,11 +101,3 @@ func StartNSWatcher(
 		logger.Info("buildermgr.NSWatcher: stopped")
 	})
 }
-
-func builderNSName(obj interface{}) string {
-	nsObj, ok := obj.(*corev1.Namespace)
-	if !ok {
-		return ""
-	}
-	return nsObj.Name
-}