This function is not called anywhere directly, and cannot be called by
the dynamic `repr_<type>()` dispatch mechanism because unicode is no
longer a type in Python 3.

…ction

This will be easier to type-check, and also somewhat clearer.

max_other is used by the superclass repr_instance, but we override it
and use maxsize instead.

The DRY savings they provide are rather small, while they make it harder
to type-check, and IMO harder to understand.