Whether to re-export the `<$>` non-method operator from `Prelude` wasn't
explicitly covered in the original AMP proposal[1], but it turns out that
not doing so forces most code that makes use of applicatives to import
`Data.Functor` or `Control.Applicative` just to get that operator into
scope.  To this end, it was proposed to add `<$>` to Prelude as well[2].

The down-side is that this increases the amount of redundant-import
warnings triggered, as well as the relatively minor issue of stealing
the `<$>` operator from the default namespace for good (although at this
point `<$>` is supposed to be ubiquitous anyway due to `Applicative`
being implicitly required into the next Haskell Report)

 [1]: https://wiki.haskell.org/Functor-Applicative-Monad_Proposal
 [2]: http://thread.gmane.org/gmane.comp.lang.haskell.libraries/24161

(cherry picked from commit eb3661f2)