docs(verification): delete deprecated canonical-campaign sections (closes #4380)

[bokelley]

Summary

PR #4387 rewrote the front-of-page framing for (Sandbox) and left the deprecated canonical-campaign content under a Warning banner pending this follow-up sweep. This PR deletes the banner and the ~100 lines of content it gated:

• Webhook ownership + the `attestation_verifier`-scoped consent requirement (compliance webhook displacement).
• Two discovery paths for (Live) — Path A Greenfield and Path B (B1 polling-only, B2 webhook-attached).
• What the compliance engine observes for (Live) — the eight-check table (Liveness, Freshness, Plausibility, Filter correctness, Reporting-surface cross-consistency, Lifecycle correctness, Introspection consistency, Seller-initiated state transitions).
• Why continuous observability for (Live) — four-bullet rationale.
• Anti-teach-to-test alignment subsection that hung off (Live); the page-level reference at `conformance#anti-teach-to-test` is untouched.
• Maintenance windows declaration block (only meaningful for a rolling-window engine).
• The multi-subscriber `reporting_webhook` supporting issue paragraph — anchored to brownfield (Live) enrollment; gone with the section.
• The `attestation_verifier` scope cross-link in "Relationship to other surfaces" — described as the scope granted to the compliance engine for (Live) observation; no longer load-bearing.

What stays

Per the issue scope, kept untouched:

• Badge mark visuals + naming history table (historical compatibility reference)
• JWT envelope claims and `/.well-known/jwks.json` decentralized verification
• Registry surfaces (SVG badge URLs, embed snippet, registry filter, brand.json enrichment)
• Eligibility, mark semantics, lifecycle, revocation, "What AAO Verified is not"
• The deferred-issues paragraph on (get_media_buys MUST return all account-owned buys regardless of creation surface #2963, Capability introspection task + attestation_verifier scope + RBAC error codes #2964, Compliance storyboards validate response shape but not filter behaviour — filtering params can silently no-op #2902) that frames them as relevant only if AAO ever returns to a canonical-campaign model

Out of scope

The mid-page sections (Mark semantics, Per-version badges, Display, Registry filter, brand.json enrichment) still use `(Live)` / `'live'` terminology rather than the new `(Sandbox)` qualifier. That's a separate consistency sweep — the issue scope here is deletion, not rename. The underlying wire-format value (`verification_modes: 'live'` in the JWT and `/api/registry` API) hasn't been renamed yet either, so the JSON examples are accurate to what the API returns today.

Test plan

• `git diff --stat` — only `docs/building/verification/aao-verified.mdx` changed, 100 deletions.
• `npm run precommit` — all unit tests, lint, and typecheck green (deletion only).
• Manually walked headings post-cut: 14 `##` sections, no orphaned anchor refs.

Closes #4380.

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