AutoTest: Code cosmetics

* use nullptr
* override
* remove old style casts
* fix most of the code model warnings

Change-Id: Ia08e846f9326ae28ca7e7d66748e25a8b817b9b1
Reviewed-by: Xing Xiong
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/autotest/qtest/qttestsettingspage.cpp

@@ -65,8 +65,6 @@ void QtTestSettingsWidget::setSettings(const QtTestSettings &settings)
     case MetricsType::Perf:
         m_ui.perfRB->setChecked(true);
         break;
-    default:
-        m_ui.walltimeRB->setChecked(true);
     }
 }