Fix _configuration_file argument getting passed to model
# What does this PR do?

Currently, the following code fails:
```
from transformers import LayoutLMv2ForTokenClassification
model = LayoutLMv2ForTokenClassification.from_pretrained('microsoft/layoutxlm-base', num_labels=10)
```
or any code using this checkpoint.

This is because the `_configuration_file` argument passed to the config ends up in the kwargs passed to the model. This PR fixes that and adds a test to make sure we don't regress.

Pb was reported in #15451
_The documentation is not available anymore as the PR was closed or merged._