It is enough to go to this “conference” settings > Room Creation Permissions and switch it to “Only specific users can create a chat room.” without adding any users. Then nobody will be able to create rooms. Will get an error from the server.
You can also delete it, nothing bad will happen. You will be able to create a new one, if you need it. In this case usually clients won’t get an error when trying to create a room (e.g. Spark). Just nothing will happen while pressing the button. Also Spark’s room browser will list other services instead of the rooms. I think first option is better.