Unlinks Zuper products from this supplier: for each product in zuper_product_uid, every catalog row linking it to the supplier is removed from all of the provider's saved branches, and the product is no longer marked as linked to the supplier. If a branch loses its last row for a product and that branch was the product's preferred vendor, the preferred vendor is cleared. Every listed product must currently be linked to this supplier with at least one catalog row, otherwise the request fails with 400 and nothing is removed; UIDs that match no product are ignored as long as at least one does. Admin only: the API key must belong to an admin user; other roles receive 405 Access Denied.