TreeModel: Introduce a destroyItem() convenience function

Shorthand for delete takeItem(...).

Change-Id: Icb7b60e5c19aa0d21650eefff65f7eb55e9f90b0
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/cmakeprojectmanager/cmakesettingspage.cpp

@@ -242,7 +242,7 @@ void CMakeToolItemModel::removeCMakeTool(const Core::Id &id)
     CMakeToolTreeItem *treeItem = cmakeToolItem(id);
     QTC_ASSERT(treeItem, return);
 
-    delete takeItem(treeItem);
+    destroyItem(treeItem);
     m_removedItems.append(id);
 }