`TcRnUserTypeError` 47403 should be folded into `UserTypeError` 64725

`TcRnUserTypeError` (47403) and `UserTypeError` (64725) really are the same error, but they get triggered in different parts of the compiler. At first I thought one was specifically for constraints and the other one for type families, but it's more subtle than that (in some cases, adding/removing a type signature changes which one you get), but for the user it really doesn't make a difference. If they had the same error code, that wouldn't be a problem. Another alternative would be to allow redirections, so e.g. the link for `TcRnUserTypeError` (47403) simply redirects to the page for `UserTypeError` (64725).