enhance(ad-free): hide all banners completely (#11787)

When paying MDN Plus subscribers enable the "Ad-free experience", we now
hide all banners completely, rather than displaying empty sections.

Author: caugner

Diff for: client/src/ui/organisms/placement/index.scss

@@ -272,6 +272,10 @@ section.place {
       width: initial;
     }
   }
+
+  html[data-nop] & {
+    display: none;
+  }
 }
 
 .dark section.place .pong-box2 {