Migrate the remaining parts of the exposed API to GhcMod a

Language/Haskell/GhcMod/List.hs

@@ -1,4 +1,4 @@
-module Language.Haskell.GhcMod.List (listModules, modules) where
+module Language.Haskell.GhcMod.List (modules) where
 
 import Control.Applicative ((<$>))
 import Control.Exception (SomeException(..))
@@ -12,10 +12,6 @@ import UniqFM (eltsUFM)
 
 ----------------------------------------------------------------
 
--- | Listing installed modules.
-listModules :: Options -> Cradle -> IO String
-listModules opt _ = runGhcMod opt $ modules
-
 -- | Listing installed modules.
 modules :: GhcMod String
 modules = do