The Overflow anchor is displayed by design even of there are no overflow items.
If you want to hide it based on some condition, I can suggest using CSS and custom CSS class which will be added when the anchor has to be hidden. You can use a similar CSS selector in order to access the needed DOM element:
Then use jQuery to add and remove the custom CSS class from the NavBar:
I hope this will help to achieve the desired result.
Telerik by Progress