qt: Default destructors where applicable

Makes code consistent with our style of defaulting special member
functions where applicable.

src/yuzu/about_dialog.cpp

@@ -15,4 +15,4 @@ AboutDialog::AboutDialog(QWidget* parent) : QDialog(parent), ui(new Ui::AboutDia
                                        Common::g_scm_desc, QString(Common::g_build_date).left(10)));
 }
 
-AboutDialog::~AboutDialog() {}
+AboutDialog::~AboutDialog() = default;