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

Follows from GHC D1460.

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