Remove redundant Functor constraint from StateT Applicative/Alternative instances

[Henning Thielemann]

On Mon, 21 Nov 2016, Baldur Blöndal wrote:

> Does this belong here? Applicative [1] and Alternative [2] instances of StateT have redundant constraints
> 
> > instance (Functor m, Monad     m) => Applicative (StateT s m)
> > instance (Functor m, MonadPlus m) => Alternative (StateT s m)
> 
> The Functor constraint may be removed

Only since the AMP, i.e. GHC-7.10.