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This PR bumps the client tests from `google/flan-t5-xxl` to
`meta-llama/Llama-2-7b-chat-hf` to resolve issues when calling the
endpoint and `google/flan-t5-xxl` is not available

run with
```bash
make python-client-tests

clients/python/tests/test_client.py ..............     [ 43%]
clients/python/tests/test_errors.py ..........         [ 75%]
clients/python/tests/test_inference_api.py ......      [ 93%]
clients/python/tests/test_types.py ..                  [100%]
```

**note `google/flan-t5-xxl` function is currently unused but still
included in the `conftest.py`

This reverts commit 2d56f106.

It causes a breaking in our integrations-tests.

# What does this PR do?
Since
([#1097](https://github.com/huggingface/text-generation-inference/pull/1097))
the clients do not need to specify a max_length anymore. However, the
python client in this repo had not yet been adapted to these changes.
This PR makes it possible to use the python client and not provide
max_new_tokens.

<!-- Remove if not applicable -->


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [x] Did you read the [contributor
guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the
[forum](https://discuss.huggingface.co/)? Please add a link
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Here are the
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- [x] Did you write any new necessary tests?


## Who can review?

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members/contributors who may be interested in your PR.

Close #288