Mesh: modernize C++: use equals default

src/Mod/Mesh/Gui/DlgDecimating.cpp

@@ -48,9 +48,7 @@ DlgDecimating::DlgDecimating(QWidget* parent, Qt::WindowFlags fl)
     onCheckAbsoluteNumberToggled(false);
 }
 
-DlgDecimating::~DlgDecimating()
-{
-}
+DlgDecimating::~DlgDecimating() = default;
 
 bool DlgDecimating::isAbsoluteNumber() const
 {
@@ -136,11 +134,6 @@ TaskDecimating::TaskDecimating()
     }
 }
 
-TaskDecimating::~TaskDecimating()
-{
-    // automatically deleted in the sub-class
-}
-
 bool TaskDecimating::accept()
 {
     std::vector<Mesh::Feature*> meshes = Gui::Selection().getObjectsOfType<Mesh::Feature>();