Tidy up tutorial preamble

doc/tutorial.ipynb

@@ -28,49 +28,6 @@
     "and a link to our chat room, where you can ask questions about Thunor."
    ]
   },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "## A note about online documentation\n",
-    "\n",
-    "This documentation is available [online](https://core.thunor.net) or by\n",
-    "building it locally. Unforunately, there is [a known issue](https://github.com/rtfd/sphinx_rtd_theme/pull/545)\n",
-    "that sometimes prevents some of the plots below from displaying online. We're\n",
-    "awaiting a fix from our documentation host, readthedocs. In the meantime,\n",
-    "please try refreshing the page, or you can [build the documentation locally as described in the README](https://github.com/alubbock/thunor). The latter approach is recommended,\n",
-    "since as it gives you a chance to edit and extend this Jupyter Notebook\n",
-    "to explore how Thunor Core works."
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "### [Ignore] Set up code for online documentation"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "# Temporary hack, see https://github.com/poliastro/poliastro/issues/281\n",
-    "from IPython.display import HTML\n",
-    "HTML('<script type=\"text/javascript\" src=\"https://cdnjs.cloudflare.com/ajax/libs/require.js/2.1.10/require.min.js\"></script>')"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "import sys, os\n",
-    "sys.path.insert(0, os.path.abspath('../'))"
-   ]
-  },
   {
    "cell_type": "markdown",
    "metadata": {},