A quick scan of their Contract of Carriage indicates nothing which applies to removal of passengers in good standing after they've boarded. There are a bunch of conditions dealing with removal of boarded passengers because of violence, drugs, not going through security, use of illicit substances, etc., but nothing which talks about removing boarded passengers simply because the airline feels they need the seat for someone else. It does address refusal of boarding privileges for any number of reasons but does so in the implied context of "before you set foot on the plane". It addresses voluntary deplaning in various ways but doesn't mention that "voluntary" may also include having your face smashed in and being dragged down the aisle by uniformed officers.
Brad