DS-3406: Ordering sub communities and collections

dspace-api/src/main/java/org/dspace/content/ItemServiceImpl.java

@@ -656,7 +656,7 @@ public class ItemServiceImpl extends DSpaceObjectServiceImpl<Item> implements It
         }
 
         //Only clear collections after we have removed everything else from the item
-        item.getCollections().clear();
+        item.clearCollections();
         item.setOwningCollection(null);
 
         // Finally remove item row