lang: funcs: funcgen: Refactor slightly for list input

This code had some design issues. We'll rewrite this eventually, but for
now, let's allow list inputs. Refactor this to make it possible.

lang/funcs/funcgen/func.go

@@ -143,7 +143,7 @@ func (obj *function) Signature() (string, error) {
 
 // MakeGoReturn returns the golang signature of the return.
 func (obj *function) MakeGoReturn() (string, error) {
-	return obj.Return[0].ToGolang()
+	return obj.Return[0].OldToGolang()
 }
 
 // ConvertStart returns the start of a casting function required to convert from