[Backup] az backup container register: Revert managed identity support for Azure Files backup

[Ethan Yang (necusjz)]

Reverts #34109

[Yong Zhang (yonzhan)]

Thank you for your contribution! We will review the pull request and get back to you soon.

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation consistently reverts the command surface, behavior, documentation, and associated tests from #34109.

Review effort: Balanced
Findings: None

What changed in this PR

Reverts #34109, restoring the previous Azure Files backup behavior.

Changes:

• Removes managed-identity registration, protection, and restore support.
• Removes cross-subscription Azure Files restore support.
• Removes associated parameters, help examples, formatting, and tests.

File	Description
_client_factory.py	Restores subscription-context client factories.
_format.py	Removes identity fields from container output.
_help.py	Removes reverted feature examples.
_params.py	Removes managed-identity and cross-subscription arguments.
commands.py	Restores the workload registration handler.
custom_afs.py	Restores prior registration and restore behavior.
custom_base.py	Removes routing and parameters for reverted functionality.
test_afs_commands.py	Removes the managed-identity scenario test.
test_custom_afs.py	Removes feature-specific unit tests.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[Yong Zhang (yonzhan)]

Backup