Use GhcModT everywhere and remove the GhcMod alias

Not doing this makes having GhcModT pretty pointless as users of the
library wouldn't be able to use custom inner monads as evey function for
dealing with GhcModT's would be constraint to (GhcModT IO) thus only
allowing IO as the inner monad.

Language/Haskell/GhcMod/CaseSplit.hs

@@ -33,10 +33,11 @@ data SplitToTextInfo = SplitToTextInfo { sVarName     :: String
                                        }
 
 -- | Splitting a variable in a equation.
-splits :: FilePath     -- ^ A target file.
+splits :: IOish m
+       => FilePath     -- ^ A target file.
        -> Int          -- ^ Line number.
        -> Int          -- ^ Column number.
-       -> GhcMod String
+       -> GhcModT m String
 splits file lineNo colNo = ghandle handler body
   where
     body = inModuleContext file $ \dflag style -> do