Remove dead cloudant_fake stub module

[bhargavikvmpl-2001]

Summary

cloudant_fake.py defined two no-op stand-ins (CloudantV1, CouchDbSessionAuthenticator) used as a Python 3.9 mypy fallback while ibmcloudant was excluded on that version. #52072 dropped Python 3.9 support and the hook now imports both classes directly from ibmcloudant, leaving the stub unreachable.

A repo-wide search confirms no remaining references to cloudant_fake outside its own entry in the OVERLOOKED_TESTS allowlist in test_project_structure.py.

• Deleted providers/cloudant/src/airflow/providers/cloudant/cloudant_fake.py
• Removed its OVERLOOKED_TESTS entry in airflow-core/tests/unit/always/test_project_structure.py

Closes #72269

Test plan

Docker/breeze wasn't available in my environment, so I verified both of the issue's required checks by other means against the actual repo:

• test_providers_modules_should_have_tests — replicated the test's exact algorithm as a standalone script against the live filesystem: missing_tests_files and added_test_files both come back empty.
• mypy on providers/cloudant/src/airflow/providers/cloudant — installed mypy + ibmcloudant in an isolated venv and ran mypy scoped to the 5 cloudant source files: Success: no issues found in 5 source files.
• Confirmed via GitHub code search and a fresh local grep that cloudant_fake has zero remaining references anywhere in the repo.

🤖 Generated with Claude Code

[boring-cyborg]

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[shahar1]

Thanks for your contribution!
As #72457 preceeded this PR and solves this issue the exact same way - I'll merge the former.
Feel free to solve other open issues.