Unneeded closure argument in example notebook

In the Readout example, a closure is handed into the `analyze` function: 
https://github.com/BioroboticsLab/IBA/blob/master/notebooks/pytorch_IBA_train_readout.ipynb

```
model_loss_closure = lambda x: -torch.log_softmax(model(x), 1)[:, target].mean()
heatmap = iba.analyze(img[None].to(dev), model_loss_closure) 
```

This is probably not needed