A federal appeals court threw out the death sentence imposed on a convicted murderer who was forced to wear a “stun belt” during the penalty phase of his trial.The 7th U.S. Circuit Court of Appeals on Friday held John M. Stephenson’s trial counsel bungled the job by failing to object to the use of the belt in the absence of evidence that he “would go berserk in the courtroom.”A panel of the court wrote the belt — which allows an officer to send an electric shock to a prisoner who creates …