Folllowing up MDL-77924 for which a variety of module could potentially launch a cryptic exception when the module was disabled and existed in the course to be deleted, this ticket is taking care of the more specific case of BigBlueButtonBN.

The issue here is in the way we use the instance class for a lot of different use case in the 
bigbluebuttonbn_delete_instance function (lib.php).
We use it for:

1. Finding the meeting id (so we can close meeting which are still open)
2. Log the deleted event

The issue being that the instance incorporates the course module (cm_info) definition but this information is not available when the module is disabled (get_fast_modinfo will not return any disabled module instance).

So we need to change the API of the instance class and check if this has no impact anywhere else.