Refactor BoringFabric in tests

[awaelchli]

What does this PR do?

Removes the BoringFabric pattern. It's only used by the few FSDP end2end tests.
Fixes #17479

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📚 Documentation preview 📚: https://pytorch-lightning--19364.org.readthedocs.build/en/19364/

cc @justusschock @awaelchli @carmocca @Borda

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 lightning_fabric: CPU workflow

Check ID	Status
fabric-cpu (macOS-11, lightning, 3.8, 1.13, oldest)	success	✅
fabric-cpu (macOS-11, lightning, 3.10, 1.13)	success	✅
fabric-cpu (macOS-11, lightning, 3.10, 2.0)	success	✅
fabric-cpu (macOS-11, lightning, 3.11, 2.1)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.8, 1.13, oldest)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.10, 1.13)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.10, 2.0)	success	✅
fabric-cpu (ubuntu-20.04, lightning, 3.11, 2.1)	success	✅
fabric-cpu (windows-2022, lightning, 3.8, 1.13, oldest)	success	✅
fabric-cpu (windows-2022, lightning, 3.10, 1.13)	success	✅
fabric-cpu (windows-2022, lightning, 3.10, 2.0)	success	✅
fabric-cpu (windows-2022, lightning, 3.11, 2.1)	success	✅
fabric-cpu (macOS-11, fabric, 3.8, 1.13)	success	✅
fabric-cpu (ubuntu-20.04, fabric, 3.8, 1.13)	success	✅
fabric-cpu (windows-2022, fabric, 3.8, 1.13)	success	✅
fabric-cpu (macOS-12, fabric, 3.11, 2.0)	success	✅
fabric-cpu (macOS-12, fabric, 3.11, 2.1)	success	✅
fabric-cpu (ubuntu-22.04, fabric, 3.11, 2.0)	success	✅
fabric-cpu (ubuntu-22.04, fabric, 3.11, 2.1)	success	✅
fabric-cpu (windows-2022, fabric, 3.11, 2.0)	success	✅
fabric-cpu (windows-2022, fabric, 3.11, 2.1)	success	✅

These checks are required after the changes to tests/tests_fabric/helpers/datasets.py, tests/tests_fabric/helpers/models.py, tests/tests_fabric/strategies/test_deepspeed_integration.py, tests/tests_fabric/strategies/test_fsdp_integration.py, tests/tests_fabric/strategies/test_xla.py, tests/tests_fabric/strategies/test_xla_fsdp_integration.py, tests/tests_fabric/utilities/test_data.py.

🟢 lightning_fabric: Azure GPU

Check ID	Status
lightning-fabric (GPUs) (testing Fabric | latest)	success	✅
lightning-fabric (GPUs) (testing Lightning | latest)	success	✅

These checks are required after the changes to tests/tests_fabric/helpers/datasets.py, tests/tests_fabric/helpers/models.py, tests/tests_fabric/strategies/test_deepspeed_integration.py, tests/tests_fabric/strategies/test_fsdp_integration.py, tests/tests_fabric/strategies/test_xla.py, tests/tests_fabric/strategies/test_xla_fsdp_integration.py, tests/tests_fabric/utilities/test_data.py.

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[codecov]

Codecov Report

Merging #19364 (3586ae7) into master (6018b07) will decrease coverage by 54%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #19364      +/-   ##
==========================================
- Coverage      83%      29%     -54%     
==========================================
  Files         448      440       -8     
  Lines       37878    37724     -154     
==========================================
- Hits        31618    11013   -20605     
- Misses       6260    26711   +20451