Fix clusterctl error on exit

Fix code still using the close method on the Link class which was
removed in 3bccbac.

clusterctl.js

@@ -391,7 +391,7 @@ async function startControl() {
 			}
 		}
 
-		control.close("quit");
+		controlConnector.close("quit");
 		return; // ??
 	}