Adwaita: Outline radius not synced with increased border radius

See this screenshot: https://1.bp.blogspot.com/-HVcSvFYQI0k/XI0HtNYhX-I/AAAAAAAADaw/uPgPadDPHF03ubA2FRH9Uxp5WhJdcb6jgCLcBGAs/s1600/about.png

Alternative: Convince @otte that we get rid of -gtk-outline-radius and instead fixate it to the border radius in use.