Reference model step count directly for markdown output

per @rht feedback

Author: rlskoeser

mesa/experimental/jupyter_viz.py

@@ -181,14 +181,9 @@ def make_model():
     # 3. Buttons
     playing = solara.use_reactive(False)
 
-    # 4. Status indicators
-    #: current round step count
-    step = solara.use_reactive(True)
-
     def on_value_play(change):
         if viz.model.running:
             viz.do_step()
-            step.value = viz.model.schedule.steps
         else:
             playing.value = False
 
@@ -212,7 +207,7 @@ def on_value_play(change):
             playing=playing.value,
             on_playing=playing.set,
         )
-        solara.Markdown(md_text="**Step:** %d" % step.value)
+        solara.Markdown(md_text=f"**Step:** {viz.model.schedule.steps}")
         # threaded_do_play is not used for now because it
         # doesn't work in Google colab. We use
         # ipywidgets.Play until it is fixed. The threading