Replace dt with opt.timestep.

PiperOrigin-RevId: 636984197
Change-Id: I2b5eaae0c5e5be840f93c4fe8f725884959703cd

mjx/tutorial.ipynb

@@ -977,7 +977,7 @@
     "    path = epath.Path('mujoco_menagerie/google_barkour_vb/scene_mjx.xml')\n",
     "    sys = mjcf.load(path.as_posix())\n",
     "    self._dt = 0.02  # this environment is 50 fps\n",
-    "    sys = sys.tree_replace({'opt.timestep': 0.004, 'dt': 0.004})\n",
+    "    sys = sys.tree_replace({'opt.timestep': 0.004})\n",
     "\n",
     "    # override menagerie params for smoother policy\n",
     "    sys = sys.replace(\n",
@@ -1448,7 +1448,7 @@
    },
    "outputs": [],
    "source": [
-    "HTML(html.render(eval_env.sys.replace(dt=eval_env.dt), rollout))"
+    "HTML(html.render(eval_env.sys.tree_replace({'opt.timestep': eval_env.dt}), rollout))"
    ]
   }
  ],