Update to clang-16

Use runner Ubuntu 22.04 for clang-16
Remove unused code detected by clang-16

ApplicationLibCode/UserInterface/RiuMainWindow.cpp

@@ -1765,7 +1765,6 @@ void RiuMainWindow::updateMemoryUsage()
 
     QColor okColor( 0, 150, 0 );
     QColor warningColor( 200, 0, 0 );
-    QColor criticalColor( 255, 100, 0 );
 
     float currentUsageFraction = 0.0f;
     float availVirtualFraction = 1.0f;