Remove unused variable

IPython/terminal/interactiveshell.py

@@ -203,7 +203,6 b' class TerminalInteractiveShell(InteractiveShell):'
 
     @observe("editing_mode")
     def _editing_mode_changed(self, change):
-        u_mode = change.new.upper()
         if self.pt_app:
             self.init_prompt_toolkit_cli()