Add workaround for #2710 (#2711)

Remove subsection "Initial conditions" in notebook to fix RTD build

docs/rxd-tutorials/extracellular.ipynb

@@ -428,31 +428,6 @@
    "metadata": {},
    "source": [
     "### Inhomogeneities\n",
-    "#### Initial conditions\n",
-    "Initial condition in the ECS need not be a scalar concentration. Suppose we only want to apply the buffer shown above to a sphere in the middle of the ECS, this can be achieved by passing function that takes a node as an argument."
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "del A, buffering\n",
-    "A = rxd.Species(\n",
-    "    ecs,\n",
-    "    name=\"buffer\",\n",
-    "    charge=1,\n",
-    "    d=0,\n",
-    "    initial=lambda nd: 10 if (nd.x**2) + (nd.y**2) + nd.x**2 < 25**2 else 0,\n",
-    ")\n",
-    "buffering = rxd.Reaction(k + A, AK, kf, kb)"
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
     "#### Anisotropy\n",
     "The diffusion coefficient for a species can be different in each direction. e.g. to limit diffusion to the x,y-plane;"
    ]