fix: don't move model to device under other dist train backends

[excepshenal]

What does this PR do?

Under fp16_full_eval or bf16_full_eval, still don't move model to device if using another dist train backend.

This is causing bugs with FSDP2 + bf16_full_eval. The dist train backend would still be in charge of moving model to device.

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

@SunMarc