Update legacy API usage in get_started.ipynb

[james47]

Motivation for features / changes

As title. Current code no longer runs in the newer TF version (2.17.0 on Colab) with the following error / warning:

AttributeError                            Traceback (most recent call last)
[<ipython-input-19-f1056f2ad84b>](https://localhost:8080/#) in <cell line: 5>()
     24 
     25   # Reset metrics every epoch
---> 26   train_loss.reset_states()
     27   test_loss.reset_states()
     28   train_accuracy.reset_states()

AttributeError: 'Mean' object has no attribute 'reset_states'

/usr/local/lib/python3.10/dist-packages/keras/src/layers/reshaping/flatten.py:37: UserWarning: Do not pass an `input_shape`/`input_dim` argument to a layer. When using Sequential models, prefer using an `Input(shape)` object as the first layer in the model instead.
  super().__init__(**kwargs)

Technical description of changes

N/A

Screenshots of UI changes (or N/A)

N/A

Detailed steps to verify changes work correctly (as executed by you)

Run on Colab

Alternate designs / implementations considered (or N/A)

N/A

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB