[aur-general] pandoc moved back to the AUR for the time being

I've moved pandoc back to the AUR because the latest version picked up too many new dependencies. It was convenient to have it in [community], but it's much saner to maintain these with the automation used by the arch-haskell project. I only use it for Rust's documentation generator, and don't want to be frequently rebuilding 30+ libraries for a language I don't use. Our packaging standards don't make much sense for Haskell because there are little gains from dynamic linking. There's not nearly enough sharing of code for it to come close to being efficient, and no stable ABI either.