Remove `MarkupLMForMaskedLM` from `MAPPING`
# What does this PR do?

There is no `MarkupLMForMaskedLM`.

BTW, could we check if the arguments passed to the recursive call are identical to the inputs: if so, don't call recursively.
https://github.com/huggingface/transformers/blob/4edb3e49f6bd3d1a4f6862452ecaf07108d62ff7/src/transformers/models/auto/auto_factory.py#L548-L558

I  can work on that if you are OK, @sgugger .

I freak out when I see
```bash
RecursionError: maximum recursion depth exceeded while calling a Python object
```
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