haskell-uhc: remove package

UHC has not seen commits since 2012. The first issue is that it needs an
older fgl. Easily ammended. The second issue is that it relies on a
broken FunctionalDependencies behaviour which was fixed with 7.8.3 which
means it's non-trivial to patch. I suspect no one with 7.8.3 has had it
running.