As a follow up of MDL-74965
1. Add a new role derived from student (let's say superstudent)

2. Add a new BigbluebuttonBN activity
3. Remove all Roles assignment
4. Add a role assignment based on this role and the "Moderator" role
5- As an admin, delete the role superstudent
6- Go back to settings in the activity
7- The participant list/ role assignment is empty  (this is not happenign anymore because the fix MDL-74965 has been applied)
8. If you inspect the HTML code, the input named "participant" has still the deleted role in its JSON encoding of the rule value.

The issue being that whenever a role disappear editing the Bigbluebutton activity does not remove the missing role from the list.