Eliminate support for deprecated GADT syntax
Eliminate support for deprecated GADT syntax

Follows from GHC D1460.

niteria/haddock,Fuuzetsu/haddock,randen/haddock,idontgetoutmuch/haddock,randen/haddock,Helkafen/haddock,Fuuzetsu/haddock,niteria/haddock,haskell/haddock,haskell/haddock,Helkafen/haddock,haskell/haddock,Helkafen/haddock,niteria/haddock,idontgetoutmuch/haddock,haskell/haddock,haskell/haddock,Fuuzetsu/haddock,Fuuzetsu/haddock,randen/haddock,idontgetoutmuch/haddock