FixAuxiliaryLossForDeformableDetr
Author: long8v
Pull request: yes

# What does this PR do?
DeformableDetr does not work when auxiliary_loss=True.
Since Deformable Detr has list of class_embed, bbox_embed, this code will raise NotImplementedError.
```python
                intermediate = outputs.intermediate_hidden_states if return_dict else outputs[4]
                outputs_class = self.class_embed(intermediate)
                outputs_coord = self.bbox_embed(intermediate).sigmoid()
```
```python
outputs_class = self.class_embed(intermediate)
File "/opt/conda/lib/python3.8/site-packages/torch/nn/modules/module.py", line 1110, in _call_impl
return forward_call(*input, **kwargs)
File "/opt/conda/lib/python3.8/site-packages/torch/nn/modules/module.py", line 201, in _forward_unimplemented
raise NotImplementedError
NotImplementedError
```
To fix this, we can simply use predefined `outputs_class` and `outputs_coord` in this [line](https://github.com/huggingface/transformers/blob/main/src/transformers/models/deformable_detr/modeling_deformable_detr.py#L1943-L1944).

## Before submitting
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      to it if that's the case.
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- [ ] Did you write any new necessary tests?


## Who can review?

@NielsRogge 

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

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@NielsRogge Ping on this PR.

Hi @long8v would you be able to run `make fixup` from the root of the repo, and potentially rebase on the main branch to make the CI green?

Thanks!

I reuploaded this PR [here](https://github.com/huggingface/transformers/pull/20959)!