Remove the temporary iSCSI compatibility dependency after V2 migration #5781

🤖 Generated by the Agentic Engineer

The maintainer directed on 2026-11-02 that production volumes must move to released Longhorn V2 without waiting for upstream changes. Keep the real iSCSI host package temporarily because Longhorn 1.13.0 still checks it during startup and upgrades, even when the data path uses V2. This compatibility dependency must not block the volume migration in #5582.

Track released V2-only prerequisite support here, including longhorn/longhorn#14438, manager PR longhorn/longhorn-manager#5458, CLI PR longhorn/cli#673, and chart PR longhorn/longhorn#14440. These contributions are not deployed fixes. Follow upstream progress from this portfolio issue; create no auxiliary upstream maintenance work.

Acceptance: verify a supported release covers startup, upgrade and host monitoring with V1 disabled; update the declarative host image and future-node definitions; roll every node class safely; observe no iSCSI extension or active session while all production volumes remain healthy on V2. Preserve recovery data and use the normal protected delivery path. Resume removal when released support and the V1 retirement proofs are available.

Part of #5582.