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.

I propose we simply remove it. I think in theory one should be able to compile it with something like 7.4.2 but 7.4.2 will have a very tough time trying to compile the modern versions of UHC's dependencies.