Clean-up BERT-BASE FSDP test

[vivekgoe]

What does this PR do?

Clean-up flags from bert-base FSDP flags.

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[astachowiczhabana]

huggingface#831