Delete deprecated ChatDataset and InstructDataset

[joecummings]

Context

What is the purpose of this PR? Is it to

• add a new feature
• fix a bug
• update tests and/or documentation
• other (please add here)

Deleting deprecated classes ChatDataset and InstructDataset, which have now been in the release for a cycle. Closes #1780.

Changelog

What are the changes made in this PR?

• Delete ChatDataset and InstructDataset
• Update references and tests

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UX

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• I did not change any public API
• I have added an example to docs or docstrings

[pytorch-bot]

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[SalmanMohammadi]

torchtune/docs/source/deep_dives/configs.rst L122

.. code-block:: python

    # Note the API of the tokenizer we specified - we need to pass in a path
    def llama2_tokenizer(path: str) -> Llama2Tokenizer:

    # Note the API of the dataset we specified - we need to pass in a model tokenizer
    # and any optional keyword arguments
    def alpaca_dataset(
        tokenizer: ModelTokenizer,
        train_on_input: bool = True,
        max_seq_len: int = 512,
    ) -> InstructDataset:

    from torchtune import config

    # Since we've already specified the path in the config, we don't need to pass
    # it in
    tokenizer = config.instantiate(cfg.tokenizer)
    # We pass in the instantiated tokenizer as the first required argument, then
    # we change an optional keyword argument
    dataset = config.instantiate(
        cfg.dataset,
        tokenizer,
        train_on_input=False,
    )

[SalmanMohammadi]

Line below still contains a reference to InstructDataset.

[joecummings]

whoop