Remove "inputs" in tf common test script (no longer required)
# What does this PR do?

The blocks appeared in `test_modeling_tf_common.py`

```
            # need to rename encoder-decoder "inputs" for PyTorch
            if "inputs" in pt_inputs_dict and self.is_encoder_decoder:
                pt_inputs_dict["input_ids"] = pt_inputs_dict.pop("inputs")
```
was introduced in #3547.

The PR #8602 changed `inputs` back to `input_ids` (particularly in `TFT5` model). The above block is longer necessary.

This PR removes it to avoid confusion (in particular, not to be confused with the new introduced `inputs` in PyTorch `generate`, which is expected to be applied to TF's `generate` too in the near future).
_The documentation is not available anymore as the PR was closed or merged._<|||||>> Thank you @ydshieh !
> 
> To double-check, before merging -- can you confirm that this particular test is successful for a few models? (e.g. `RUN_PT_TF_CROSS_TESTS=1 py.test tests/test_modeling_tf_bert.py)`

Hi, @gante I run it with BERT, BART and GPT2 --> all pass.

(I believe that these tests are already run by CI, see https://app.circleci.com/pipelines/github/huggingface/transformers/33021/workflows/63e4488b-7d35-46ee-9209-5e036adfe6ba/jobs/347995/parallel-runs/0/steps/0-112)