[remove redundant case covered by mapValVal in substitution code
John Meacham <john@repetae.net>**20070608035715] hunk ./Grin/SSimplify.hs 216
-    f (NodeC t vs) = do
-        vs' <- mapM f vs
-        return $ NodeC t vs'
-    f x = return x
+    f x = mapValVal f x