Remove vapoursynth-plugin-lsmashsource

[Extarys]

Plugin doesn't exist on Arch repo anymore.

Fix #850

[Extarys]

Afterthought: maybe we should add vapoursynth-plugin-bestsource...

[shssoichiro]

I wouldn't necessarily recommend bestsource as the first choice. Its indexing is very slow, and it tends to sometimes do weird things with guessing framerate (though recent releases have been working on fixing this). Though it would probably be a good idea to have instructions for each of the possible source plugins.

Which, for lsmashsource would be to get the git package from the AUR. It's strange to me that the Arch maintainers removed the stable version from the official repos.

[shssoichiro]

It looks like we need this removed in order to fix the CI build... We'll need to figure out an alternative solution at some point. I think the ideal is setting up the build to get vapoursynth-plugin-lsmashsource-git from the AUR, but that can come in a later change. For now, I'll go ahead and merge this so the CI failure isn't blocking everything.