Move Data.Functor.Contravariant from the contravariant package to base.
Since base is the bottom of the dependency hierarchy, several instances
have been removed. They will need to be added to the following packages:
transformers, StateVar, and possibly tagged. There may not actually have
been any types from tagged that previous had instanced provided by this
module though, since it may have only been used for Data.Proxy. Additionally,
all CPP has been removed. Derived Typeable instances have been removed
(since Typeable is now automatically derived for everything). The language
extension Safe is still used, although it is unclear to ATM whether or not
it is necessary.
This resolves trac issue Trac #14767.