[Examples][Flax] AttributeError: 'DataTrainingArguments' object has no attribute 'test_file'
## Description

While running run_summarization_flax.py with local files, currently we have only two DataTrainingArguments, one for training and another for validation file still we are validating test_file which is producing an error
```
Traceback (most recent call last):
  File "transformers/examples/flax/summarization/run_summarization_flax.py", line 808, in <module>
    main()
  File "transformers/examples/flax/summarization/run_summarization_flax.py", line 352, in main
    if data_args.test_file is not None:
AttributeError: 'DataTrainingArguments' object has no attribute 'test_file'
```

## Environment info
- `transformers` version: 4.9.0(master branch)
- Platform: TPU VM
- Python version: 3.9
- PyTorch version (GPU?):
- Tensorflow version (GPU?):
- Using GPU in script?:
- Using distributed or parallel set-up in script?:



### Who can help
@sgugger, @patil-suraj

### Possible Fix:
Either we can add test_file argument or remove test file validation section https://github.com/huggingface/transformers/blob/7d6285a921a23c06169e2d90c94faa0d92d00d78/examples/flax/summarization/run_summarization_flax.py#L352-L354

