fix(agents): dedupe canary skill in release-engineer frontmatter (#190)

Staff Engineer's autonomous review of PR #186 caught this — `canary` was
listed twice in skills:, leftover from the rebase that combined ohld's
role-merge edit with my Stage 1 +canary,+benchmark addition.

Non-blocking (deploy.sh _sync_config.py dedupes via set()), but the YAML
should be the source of truth, not relying on downstream defensive coding.

Author: ohld

agents/release-engineer/AGENTS.md

@@ -6,7 +6,6 @@ skills:
   - canary
   - document-release
   - setup-deploy
-  - canary
   - benchmark
 ---