chore(autoreview): use the shared canonical skill

[vincentkoc]

What Problem This Solves

Repository-local autoreview copies drift and can retain retired prerequisites such as TruffleHog.

User Impact

Install autoreview once from openclaw/agent-skills using the setup linked in .agents/skills/autoreview/SKILL.md. Reviews run from this repository through that shared installation. Updating its source checkout updates all symlinked consumers; copy-mode users reinstall once. Product runtime behavior is unchanged.

Why This Change Was Made

Keep only the canonical Markdown entrypoint and remove the copied helper, fixtures, and implementation tests.

Canonical owner and preserved downstream fixes: openclaw/agent-skills#305. Shared changes belong upstream; review runs do not download or update code automatically.

Evidence

• All 17 consumer entrypoints match the canonical template; each contains no local helper or implementation tests.
• git diff --check passes; independent integration review checked callers and removed gates.
• The shared installer and helper dry runs pass from consumer repositories without TruffleHog. Canonical regression tests and review are recorded in the upstream PR.
• Product runtime suites were not run for this shared-tooling cutover.

Landing follow-up

Repository instructions explicitly retain the original P0–P3 review gate with --max-priority P3; direct invocation examples use that override. The shared entrypoint remains identical to the canonical template.