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/Find.hs

@@ -31,11 +31,11 @@ type Symbol = String
 newtype SymMdlDb = SymMdlDb (Map Symbol [ModuleString])
 
 -- | Finding modules to which the symbol belong.
-findSymbol :: Symbol -> GhcMod String
+findSymbol :: IOish m => Symbol -> GhcModT m String
 findSymbol sym = convert' =<< lookupSym sym <$> getSymMdlDb
 
 -- | Creating 'SymMdlDb'.
-getSymMdlDb :: GhcMod SymMdlDb
+getSymMdlDb :: IOish m => GhcModT m SymMdlDb
 getSymMdlDb = do
     sm <- G.getSessionDynFlags >>= browseAll
 #if MIN_VERSION_containers(0,5,0)