fix jittering in markdown in viewer beta

nerfstudio/viewer_beta/control_panel.py

@@ -270,10 +270,9 @@ def update_step(self, step):
             step: the train step to set the model to
         """
         with self.viser_server.atomic(), self.stat_folder:
-            # TODO change to a .value call instead of remove() and add, this makes it jittery
             with self.viser_server.atomic():
                 self.markdown.remove()
-                self.markdown = self.viser_server.add_gui_markdown(f"Step: {step}")
+                self.markdown.content = f"Step: {step}"
 
     def update_output_options(self, new_options: List[str]):
         """