No, Your banners are still there. We just removed the link in the side menu. The reason for that is because since v5.1.5 we recommend everyone to create banners using the new Visual Banner Creator. Ads created using this new tool have multiple cool new options and functions and are super responsive!
Of course, you can still use your old banners and even create banners like your used to before. You can find the link to the banners and adzones under the Alternative Options tab on the AD Dashboard.