Remove deadlock detection / process reconciliation logic

[awaelchli]

What does this PR do?

Deadlock detection / process reconciliation is a feature of the DDP strategy family. It is not documented, but it is turned on by default when ddp strategies are used, unless PL_RECONCILIATE_PROCESS=0 is set.

• It has reliability issues, such as that it relies on the current working directory be shared among all nodes, which is often the case but not always.
• TorchElastic already has mechanisms to detect failing processes and can prevent a hang, and can restart the job automatically. TorchElastic has been upstreamed to PyTorch recently.
• The feature is implemented and tested only for the DDP strategy. Others who inherit from DDP are not tested. Other strategies that inherit from ParallelStrategy do not have this implemented.
• With process reconciliation turned off, an exception that occurs only on one rank but not others will lead to a hang, but the error message surfaces regardless.
• The main benefit of the feature is that processes get terminated immediately and don't hang. This could save you some money for example when running in cloud instances.

Part of #16410
Closes #12797

Does your PR introduce any breaking changes? If yes, please list them.

Yes, for everyone using the ddp strategy, and anyone else that enables PL_RECONCILIATE_PROCESS=1, the feature will no longer work. However, errors

Before submitting

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• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or internal minor changes/refactorings)

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Did you have fun?

I made sure I had fun coding 🙃

cc @Borda @justusschock @awaelchli

[carmocca]

I rebased this

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 pytorch_lightning: Tests workflow

Check ID	Status
pl-cpu (macOS-11, pytorch, 3.8, 1.11)	success	✅
pl-cpu (macOS-11, pytorch, 3.9, 1.12)	success	✅
pl-cpu (macOS-11, pytorch, 3.10, 1.13)	success	✅
pl-cpu (macOS-11, pytorch, 3.8, 1.10, oldest)	success	✅
pl-cpu (ubuntu-20.04, pytorch, 3.8, 1.10)	success	✅
pl-cpu (ubuntu-20.04, pytorch, 3.9, 1.11)	success	✅
pl-cpu (ubuntu-20.04, pytorch, 3.10, 1.12)	success	✅
pl-cpu (ubuntu-20.04, pytorch, 3.10, 1.13)	success	✅
pl-cpu (ubuntu-20.04, pytorch, 3.7, 1.10, oldest)	success	✅
pl-cpu (windows-2022, pytorch, 3.9, 1.11)	success	✅
pl-cpu (windows-2022, pytorch, 3.10, 1.12)	success	✅
pl-cpu (windows-2022, pytorch, 3.10, 1.13)	success	✅
pl-cpu (windows-2022, pytorch, 3.7, 1.10, oldest)	success	✅
pl-cpu (slow, macOS-11, pytorch, 3.7, 1.11)	success	✅
pl-cpu (slow, ubuntu-20.04, pytorch, 3.7, 1.11)	success	✅
pl-cpu (slow, windows-2022, pytorch, 3.7, 1.11)	success	✅
pl-cpu (macOS-11, lightning, 3.8, 1.13)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.8, 1.13)	success	✅
pl-cpu (windows-2022, lightning, 3.8, 1.13)	success	✅

These checks are required after the changes to src/pytorch_lightning/strategies/bagua.py, src/pytorch_lightning/strategies/ddp.py, src/pytorch_lightning/strategies/fully_sharded_native.py, src/pytorch_lightning/strategies/parallel.py, src/pytorch_lightning/strategies/sharded.py, src/pytorch_lightning/trainer/call.py, src/pytorch_lightning/utilities/exceptions.py, tests/tests_pytorch/trainer/test_trainer.py.

🟢 pytorch_lightning: Azure GPU

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🟢 pytorch_lightning: Azure HPU

Check ID	Status
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These checks are required after the changes to src/pytorch_lightning/strategies/bagua.py, src/pytorch_lightning/strategies/ddp.py, src/pytorch_lightning/strategies/fully_sharded_native.py, src/pytorch_lightning/strategies/parallel.py, src/pytorch_lightning/strategies/sharded.py, src/pytorch_lightning/trainer/call.py, src/pytorch_lightning/utilities/exceptions.py, tests/tests_pytorch/trainer/test_trainer.py.

🟢 pytorch_lightning: Azure IPU

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pytorch-lightning (IPUs)	success	✅

These checks are required after the changes to src/pytorch_lightning/strategies/bagua.py, src/pytorch_lightning/strategies/ddp.py, src/pytorch_lightning/strategies/fully_sharded_native.py, src/pytorch_lightning/strategies/parallel.py, src/pytorch_lightning/strategies/sharded.py, src/pytorch_lightning/trainer/call.py, src/pytorch_lightning/utilities/exceptions.py, tests/tests_pytorch/trainer/test_trainer.py.

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🟢 mypy

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🟢 install

Check ID	Status
install-pkg (ubuntu-22.04, app, 3.7)	success	✅
install-pkg (ubuntu-22.04, app, 3.10)	success	✅
install-pkg (ubuntu-22.04, fabric, 3.7)	success	✅
install-pkg (ubuntu-22.04, fabric, 3.10)	success	✅
install-pkg (ubuntu-22.04, pytorch, 3.7)	success	✅
install-pkg (ubuntu-22.04, pytorch, 3.10)	success	✅
install-pkg (ubuntu-22.04, lightning, 3.7)	success	✅
install-pkg (ubuntu-22.04, lightning, 3.10)	success	✅
install-pkg (ubuntu-22.04, notset, 3.7)	success	✅
install-pkg (ubuntu-22.04, notset, 3.10)	success	✅
install-pkg (macOS-12, app, 3.7)	success	✅
install-pkg (macOS-12, app, 3.10)	success	✅
install-pkg (macOS-12, fabric, 3.7)	success	✅
install-pkg (macOS-12, fabric, 3.10)	success	✅
install-pkg (macOS-12, pytorch, 3.7)	success	✅
install-pkg (macOS-12, pytorch, 3.10)	success	✅
install-pkg (macOS-12, lightning, 3.7)	success	✅
install-pkg (macOS-12, lightning, 3.10)	success	✅
install-pkg (macOS-12, notset, 3.7)	success	✅
install-pkg (macOS-12, notset, 3.10)	success	✅
install-pkg (windows-2022, app, 3.7)	success	✅
install-pkg (windows-2022, app, 3.10)	success	✅
install-pkg (windows-2022, fabric, 3.7)	success	✅
install-pkg (windows-2022, fabric, 3.10)	success	✅
install-pkg (windows-2022, pytorch, 3.7)	success	✅
install-pkg (windows-2022, pytorch, 3.10)	success	✅
install-pkg (windows-2022, lightning, 3.7)	success	✅
install-pkg (windows-2022, lightning, 3.10)	success	✅
install-pkg (windows-2022, notset, 3.7)	success	✅
install-pkg (windows-2022, notset, 3.10)	success	✅

These checks are required after the changes to src/pytorch_lightning/strategies/bagua.py, src/pytorch_lightning/strategies/ddp.py, src/pytorch_lightning/strategies/fully_sharded_native.py, src/pytorch_lightning/strategies/parallel.py, src/pytorch_lightning/strategies/sharded.py, src/pytorch_lightning/trainer/call.py, src/pytorch_lightning/utilities/exceptions.py.

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[carmocca]

Pushed a commit with some leftover removals to the fsdp strategy