Remove hscolour

[andreasabel]

Malcom Wallace (@malcomwallace but I think he is no longer on github) has uploaded hscolour-1.25 to hackage: https://hackage.haskell.org/package/hscolour-1.25
So we can drop our stewardship of hscolour and delete our fork here.

The only thing is that it is unclear where the maintained sources of hscolour sit. The cabal file says http://code.haskell.org/~malcolm/hscolour but this link is dead.