Problem/Motivation
An entity type that has no bundle key (i.e. $entity_type->hasKey('bundle') === FALSE) is still able to expose multiple bundles, via hook_entity_bundle_info(). This is a logical nonsense. Not having a bundle key means: this entity type have no bundle (like the user entity type).
Proposed resolution
Don't allowhook_entity_bundle_info() (and hook_entity_bundle_info_alter()) to populate the bundle info list (see EntityTypeBundleInfo), with more than one entry which is the entity type ID itself, for such entity types.
Eventually consider deprecating such practice in the first step.
Remaining tasks
None.
User interface changes
None.
API changes
None.
Data model changes
None.
Release notes snippet
TBD.