fix loading special_tokens_map_file
Author: ZhiyuanChen
Pull request: yes

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If special tokens map have special specified, e.g.:

```python
SPECIAL_TOKENS_MAP = {
    "pad_token": {
        "content": "<pad>",
        "lstrip": False,
        "normalized": False,
        "rstrip": False,
        "single_word": False,
        "special": True,
    },
}
```

loading pretrained with special tokens map would complain:

```bash
TypeError: tokenizers.AddedToken() got multiple values for keyword argument 'special'
```

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Comments:
Hey! Which version of transformers are you using? Also which tokenizer are you trying to load? 
Special map is depracted and only kept for BC

> Hey! Which version of transformers are you using? Also which tokenizer are you trying to load? Special map is depracted and only kept for BC

Hi~ 
I'm using 4.39.3 to load an external tokenizer. 
I believe numerous codebase are still keeping the special tokens map like https://huggingface.co/facebook/esm2_t6_8M_UR50D/blob/main/special_tokens_map.json. 

> Okay! Could you just rebase on main ?

One moment

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