remove obsolete code

src/ui/content/content-ui.js

@@ -67,9 +67,7 @@ export {
 	onStartStage,
 	onEndStage,
 	onPageLoading,
-	onLoadPage,
-	onStartStageTask,
-	onEndStageTask
+	onLoadPage
 };
 
 function promptMessage(message, defaultValue) {
@@ -152,10 +150,6 @@ function onPageLoading() { }
 
 function onLoadPage() { }
 
-function onStartStageTask() { }
-
-function onEndStageTask() { }
-
 function getSelectedLinks() {
 	let selectionFound;
 	const links = [];