Remove unused imports.

src/Servant/API/Header.hs

@@ -1,8 +1,6 @@
 {-# LANGUAGE PolyKinds #-}
 module Servant.API.Header where
 
-import GHC.TypeLits
-
 -- | Extract the given header's value as a value of type @a@.
 --
 -- Example:

src/Servant/API/Sub.hs

@@ -3,7 +3,6 @@
 module Servant.API.Sub where
 
 import Data.Proxy
-import GHC.TypeLits
 
 -- | The contained API (second argument) can be found under @("/" ++ path)@
 -- (path being the first argument).