finding no plain error in the Superior Court's decision to grant the motion to withdraw the guilty plea permitting the defendant to exercise his constitutional right to a jury trial

denying Pringle’s claim that the Superior Court erred in refusing to allow Pringle to represent himself because "[t]he record, however, does not support a finding that Pringle requested to represent himself. In fact, the motion included in Pringle’s appendix reflects that, after his conviction, he requested that trial counsel be discharged and that new counsel be appointed to represent him at sentencing"