This reverts commit acb6624, reversing changes made to ba1caf0.

Revert "userdb: add birthDate field to JSON user records (#40954)"

After extensive community discussion, legal review and consideration of
privacy implications, we have decided not to implement OS-level age
attestation / age bracket signaling as initially prototyped.

Reasons for revert:

• Privacy & freedom concerns:

  • Introducing birth date storage or age queries (even local-only) creates
    a new class of sensitive user data in the OS that didn't exist before.
  • It risks normalizing permission-like checks inside the desktop session
    and could be extended to far more invasive controls in the future.

• Open Source philosophy mismatch:

  • Community-driven distributions (especially non-corporate ones) have
    neither the structure nor the desire to act as identity / age authorities.
  • Forcing account creation or age input breaks the "just works, no account
    required" experience that many users value in Linux.

• Practical & enforcement issues:

  • No reliable way to enforce truthful input without invasive verification
    (which we explicitly refuse).
  • Minimal/local implementation still exposes users to website/app blocks
    if sites decide to distrust non-signaling OSes → creates a de-facto
    requirement anyway.

• Legal / jurisdictional overreach:

  • Laws like California's AB 1043, Colorado SB 26-051 etc. appear poorly
    drafted for volunteer / decentralized projects.
  • Many distributions (MidnightBSD, Ageless Linux forks, …) already chose
    non-compliance + geo/licensing blocks instead → precedent exists to
    simply not comply rather than build half-measures.

• No upstream consensus:

  • freedesktop.org merge request closed after pushback.
  • Major distros (Ubuntu, Fedora, …) either paused, rejected or never
    committed concrete changes.
  • systemd PR remains draft/unmerged in many views.

We may revisit if:

• A zero-knowledge / cryptographic age-proof standard emerges that requires
  no birth date storage.
• Courts strike down or clarify the laws to exempt small/OSS projects.
• A truly privacy-preserving, opt-in community consensus forms.

For now: keep the system free of age-related metadata and APIs.

See-also: https://discussion.fedoraproject.org/t/california-age-verification/181968
See-also: https://blog.system76.com/post/system76-on-age-verification