Back Scribes are included in the overall depth of a cabinet. They are used to space the cabinet from the wall in case they are not plumb or a corner is out of square.
In the Edit Cabinet popup for the cabinet...
Click the menu button that applies to Back Scribe = 16mm and select Remove.
The Back Scribe kit has now been removed. You can reinstate the Back Scribe by selecting it in the Include Kits menu.