Part: modernize C++: use equals default

src/Mod/Part/Gui/DlgPartImportStepImp.cpp

@@ -50,10 +50,7 @@ DlgPartImportStepImp::DlgPartImportStepImp( QWidget* parent, Qt::WindowFlags fl
 /*
  *  Destroys the object and frees any allocated resources
  */
-DlgPartImportStepImp::~DlgPartImportStepImp()
-{
-    // no need to delete child widgets, Qt does it all for us
-}
+DlgPartImportStepImp::~DlgPartImportStepImp() = default;
 
 /*
  * public slot