[export] Cleanup the handling of has_named_sharding
has_named_sharding was introduced in #33597 and the intent
is that all exports after 1/15/2026 will have this True.
6 months later we can remove all the code paths for `not has_named_sharding`.
Here we fix a couple of places where `has_named_sharding` was not
guaranteed to set to True for new exports.
