Missing function name in `most_used_nodes.ipynb`

```python
gx = load_graph()
```

```python
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
/tmp/ipykernel_208/1558099762.py in <module>
----> 1 gx = load_graph()

NameError: name 'load_graph' is not defined
```