Full train_on_input deprecation, removing other deprecated components

[RdoubleA]

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)

Changelog

What are the changes made in this PR?

• Use masking_strategy by default in all examples and docs. Update dataset builders to use masking strategy
• Remove deprecated components init_distributed, RSOLoss, get_world_size_and_rank, torchtune/modules/tokenizers, and others

Test plan

Please make sure to do each of the following if applicable to your PR. If you're unsure about any one of these just ask and we will happily help. We also have a contributing page for some guidance on contributing.

• run pre-commit hooks and linters (make sure you've first installed via pre-commit install)
• add unit tests for any new functionality
• update docstrings for any new or updated methods or classes
• run unit tests via pytest tests
• run recipe tests via pytest tests -m integration_test
• manually run any new or modified recipes with sufficient proof of correctness
• include relevant commands and any other artifacts in this summary (pastes of loss curves, eval results, etc.)

UX

If your function changed a public API, please add a dummy example of what the user experience will look like when calling it.
Here is a docstring example
and a tutorial example

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

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/torchtune/2533

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❌ 5 New Failures, 6 Cancelled Jobs

As of commit a98e8b7 with merge base 0afea1a ():

NEW FAILURES - The following jobs have failed:

• Build Docs / build_docs (3.11) (gh)
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• GPU tests / gpu_test (3.11, stable) (gh)
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• Lint / lint (3.10) (gh)
• Recipe Tests / recipe_test (3.10) (gh)
  Process completed with exit code 2.
• Unit Test / unit_tests (3.10) (gh)
  Process completed with exit code 2.

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• GPU tests / gpu_test (3.10, stable) (gh)
  ##[error]The operation was canceled.
• GPU tests / gpu_test (3.9, stable) (gh)
  Process completed with exit code 2.
• Recipe Tests / recipe_test (3.11) (gh)
  ##[error]The operation was canceled.
• Recipe Tests / recipe_test (3.9) (gh)
  ##[error]The operation was canceled.
• Unit Test / unit_tests (3.11) (gh)
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• Unit Test / unit_tests (3.9) (gh)
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