Mesh: modernize C++11

* remove redundant void-arg
* use nullptr
* replace deprecated headers

src/Mod/Mesh/Gui/RemoveComponents.cpp

@@ -215,7 +215,7 @@ TaskRemoveComponents::TaskRemoveComponents()
 {
     widget = new RemoveComponents();
     taskbox = new Gui::TaskView::TaskBox(
-        QPixmap(), widget->windowTitle(), false, 0);
+        QPixmap(), widget->windowTitle(), false, nullptr);
     taskbox->groupLayout()->addWidget(widget);
     Content.push_back(taskbox);
 }