Remove empty cell from 11_advanced_queries.ipynb (#584)

This empty cell breaks the redisvl automation that generates the
markdown documentation

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk documentation-only change that only deletes a stray notebook
cell and does not affect library/runtime behavior.
> 
> **Overview**
> Removes a stray empty markdown cell (containing only `##`) from
`docs/user_guide/11_advanced_queries.ipynb`, preventing the
notebook-to-markdown documentation automation from breaking.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
b0be9c9. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: paoloredis

docs/user_guide/11_advanced_queries.ipynb

@@ -1278,13 +1278,6 @@
     "result_print(results)"
    ]
   },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "##"
-   ]
-  },
   {
    "cell_type": "markdown",
    "metadata": {},