Don't build xwaylandvideobridge anymore
Couple of reasons:
- Its reason for existence is diminished now that Discord supports the portal (See https://www.gamingonlinux.com/2025/01/discord-screen-sharing-with-audio-on-linux-wayland-is-officially-here)
- It's basically abandoned by its devs
- It never got a proper release
- If we want it again because its devs become active once more, getting it from Flathub (once it's packaged there) would be the more appropriate approach.