Fix sizing bug where large item bank would expand the container.

When measuring the available width, we have to hide the item bank so
that it does not expand the container.

drag_and_drop_v2/public/js/drag_and_drop.js

@@ -638,6 +638,7 @@ function DragAndDropTemplates(configuration) {
         // image to 100%, so that it doesn't expand the container.
         if (ctx.drag_container_max_width === null) {
             target_img_style.maxWidth = '100%';
+            item_bank_properties.style = {display: 'none'};
         } else {
             drag_container_style.maxWidth = ctx.drag_container_max_width + 'px';
         }