Remove release.yml: orchestration moves to saltstack-core-uploader

Release-detection and per-repo docs PRs are being centralized in the
saltstack-core-uploader repo on the Broadcom GHE, alongside the
existing watch-salt-release / saltproject-release flow. Removing this
workflow so we have a single source of truth and avoid open-PR drift
between this repo and the new orchestrator.

Author: dwoz