XLNet fails with attn_type "uni"
### System Info

- `transformers` version: 4.26.1
- Platform: Linux-5.10.104-linuxkit-aarch64-with-glibc2.17
- Python version: 3.8.16
- Huggingface_hub version: 0.12.0
- PyTorch version (GPU?): 1.13.0 (False)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: No

### Who can help?

@thomwolf 

### Information

- My own modified scripts

### Tasks

- An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)

### Reproduction

```python
from transformers import AutoModelForSequenceClassification, AutoTokenizer

model = AutoModelForSequenceClassification.from_pretrained("xlnet-base-cased")
tokenizer = AutoTokenizer.from_pretrained("xlnet-base-cased")

# Set attention type
model.transformer.attn_type = "uni"

inputs = tokenizer(["Hello, my dog is cute", "Hello, my dog is cute too"], return_tensors="pt", padding=True)
print(inputs)
outputs = model(**inputs)
```

Error:
```python-traceback
{'input_ids': tensor([[    5,    17, 11368,    19,    94,  2288,    27, 10920,     4,     3],
        [   17, 11368,    19,    94,  2288,    27, 10920,   269,     4,     3]]), 'token_type_ids': tensor([[3, 0, 0, 0, 0, 0, 0, 0, 0, 2],
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 2]]), 'attention_mask': tensor([[0, 1, 1, 1, 1, 1, 1, 1, 1, 1],
        [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]])}
Traceback (most recent call last):
  File "xlnet.py", line 70, in <module>
    outputs = model(**inputs)
  File "/usr/local/lib/python3.8/site-packages/torch/nn/modules/module.py", line 1190, in _call_impl
    return forward_call(*input, **kwargs)
  File "/home/vscode/.local/lib/python3.8/site-packages/transformers/models/xlnet/modeling_xlnet.py", line 1547, in forward
    transformer_outputs = self.transformer(
  File "/usr/local/lib/python3.8/site-packages/torch/nn/modules/module.py", line 1190, in _call_impl
    return forward_call(*input, **kwargs)
  File "/home/vscode/.local/lib/python3.8/site-packages/transformers/models/xlnet/modeling_xlnet.py", line 1161, in forward
    attn_mask += data_mask[:, :, :, None]
RuntimeError: output with shape [10, 10, 1, 1] doesn't match the broadcast shape [10, 10, 2, 1]
```

### Expected behavior

Successful forward pass with the appropriate attention masks applied.
cc @ArthurZucker and @younesbelkada <|||||>This is a fairly old model 😅 It does make sense to drop `uni` (first because it is not working and did not bother anyone) but also let's just redirect to the new [TransformerXL](https://huggingface.co/docs/transformers/model_doc/transfo-xl). Thanks for reporting<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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