Gui: modernize C++: use equals default

src/Gui/PreferencePages/DlgSettingsMacroImp.cpp

@@ -56,10 +56,8 @@ DlgSettingsMacroImp::DlgSettingsMacroImp( QWidget* parent )
 /**
  *  Destroys the object and frees any allocated resources
  */
-DlgSettingsMacroImp::~DlgSettingsMacroImp()
-{
-    // no need to delete child widgets, Qt does it all for us
-}
+DlgSettingsMacroImp::~DlgSettingsMacroImp() = default;
+
 /** Sets the size of the recent macros list from the user parameters.
  * @see RecentMacrosAction
  * @see StdCmdRecentMacros