clearer model variable naming: xlnet
Author: kamalkraj
Pull request: yes

# What does this PR do?
clearer model variable naming: xlnet

```bash
platform darwin -- Python 3.8.9, pytest-6.2.5, py-1.11.0, pluggy-1.0.0 -- /Users/kamal.raj/.virtualenvs/transformers/bin/python
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('/Users/kamal.raj/Documents/GitHub/transformers/.hypothesis/examples')
rootdir: /Users/kamal.raj/Documents/GitHub/transformers, configfile: setup.cfg
plugins: xdist-2.4.0, timeout-2.0.1, dash-2.0.0, hypothesis-6.31.3, forked-1.3.0, typeguard-2.13.2
collected 36 items                                                                                                                                                            

tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_attention_outputs <- tests/test_modeling_tf_common.py PASSED                                              [  2%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_compile_tf_model <- tests/test_modeling_tf_common.py PASSED                                               [  5%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_config PASSED                                                                                             [  8%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_determinism <- tests/test_modeling_tf_common.py PASSED                                                    [ 11%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_forward_signature <- tests/test_modeling_tf_common.py PASSED                                              [ 13%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_generate_with_headmasking <- tests/test_modeling_tf_common.py PASSED                                      [ 16%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_headmasking <- tests/test_modeling_tf_common.py PASSED                                                    [ 19%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_hidden_states_output <- tests/test_modeling_tf_common.py PASSED                                           [ 22%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_initialization <- tests/test_modeling_tf_common.py PASSED                                                 [ 25%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_inputs_embeds <- tests/test_modeling_tf_common.py PASSED                                                  [ 27%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_keras_save_load <- tests/test_modeling_tf_common.py PASSED                                                [ 30%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_keyword_and_dict_args <- tests/test_modeling_tf_common.py PASSED                                          [ 33%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_lm_head_model_beam_search_generate_dict_outputs <- tests/test_modeling_tf_common.py PASSED                [ 36%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_lm_head_model_no_beam_search_generate_dict_outputs <- tests/test_modeling_tf_common.py PASSED             [ 38%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_lm_head_model_random_beam_search_generate <- tests/test_modeling_tf_common.py PASSED                      [ 41%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_lm_head_model_random_no_beam_search_generate <- tests/test_modeling_tf_common.py PASSED                   [ 44%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_load_with_mismatched_shapes <- tests/test_modeling_tf_common.py PASSED                                    [ 47%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_loss_computation PASSED                                                                                   [ 50%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_model_common_attributes <- tests/test_modeling_tf_common.py PASSED                                        [ 52%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_model_from_pretrained PASSED                                                                              [ 55%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_model_main_input_name <- tests/test_modeling_tf_common.py PASSED                                          [ 58%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_model_outputs_equivalence <- tests/test_modeling_tf_common.py PASSED                                      [ 61%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_numpy_arrays_inputs <- tests/test_modeling_tf_common.py PASSED                                            [ 63%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_onnx_compliancy <- tests/test_modeling_tf_common.py PASSED                                                [ 66%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_onnx_runtime_optimize <- tests/test_modeling_tf_common.py PASSED                                          [ 69%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_pt_tf_model_equivalence <- tests/test_modeling_tf_common.py SKIPPED (test is PT+TF test)                  [ 72%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_resize_token_embeddings <- tests/test_modeling_tf_common.py PASSED                                        [ 75%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_save_load <- tests/test_modeling_tf_common.py PASSED                                                      [ 77%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_save_load_config <- tests/test_modeling_tf_common.py PASSED                                               [ 80%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_xlnet_base_model PASSED                                                                                   [ 83%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_xlnet_for_multiple_choice PASSED                                                                          [ 86%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_xlnet_lm_head PASSED                                                                                      [ 88%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_xlnet_qa PASSED                                                                                           [ 91%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_xlnet_sequence_classif PASSED                                                                             [ 94%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelTest::test_xlnet_token_classification PASSED                                                                         [ 97%]
tests/xlnet/test_modeling_tf_xlnet.py::TFXLNetModelLanguageGenerationTest::test_lm_generate_xlnet_base_cased PASSED                                                     [100%]

============================================================================== warnings summary ===============================================================================
../../../.virtualenvs/transformers/lib/python3.8/site-packages/flatbuffers/compat.py:19
  /Users/kamal.raj/.virtualenvs/transformers/lib/python3.8/site-packages/flatbuffers/compat.py:19: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
    import imp

-- Docs: https://docs.pytest.org/en/stable/warnings.html
============================================================ 35 passed, 1 skipped, 1 warning in 126.99s (0:02:06) =============================================================
```
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Fixes # (issue)


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [ ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
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## Who can review?

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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @LysandreJik

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
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- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

- datasets: [different repo](https://github.com/huggingface/datasets)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj
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Comments:
_The documentation is not available anymore as the PR was closed or merged._

Tagging @gante for a decorator PR!