JAX for the impatient was deleted, but it is still referenced twice

https://github.com/google/flax/blob/main/docs/guides/flax_fundamentals/flax_basics.md?plain=1#L50 and https://github.com/google/flax/blob/main/docs/guides/flax_fundamentals/flax_basics.ipynb?short_path=e8e43f2#L75 mention the "JAX for the impatient" notebook, but it was deleted in this PR: https://github.com/google/flax/pull/3434

Either "JAX for the impatient" should be restored, or those references should be deleted.

### System information

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### Problem you have encountered:

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### What you expected to happen:

Either "JAX for the impatient" should be restored, or those references should be deleted.

### Logs, error messages, etc:

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### Steps to reproduce:

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