Silan is no longer maintained upstream, so probably should be removed as
I doubt support for ffmpeg 5.0 will be added.
- Bug#1004578: silan: FTBFS with ffmpeg 5.0 Sebastian Ramacher
- Bug#1004578: silan: FTBFS with ffmpeg 5.0 Kyle Robbertze
- Bug#1004578: silan: FTBFS with ffmpeg 5.0 Sebastian Ramacher