refactor(node): delete the revocation subscriber H4 replaced

`RevocationSubscriber` kept its revocations in two in-memory sets. That is the
defect **H4** names: revocations that live only in memory mean a node restart
silently un-revokes everyone, and group revocations were dropped entirely. The
fix was the persisted `Denylist`, fed from `hub_client.maintain_ws` through
`daemon.py`'s `on_revocation`, which verifies the token against the hub key and
calls `deny_user` / `deny_group`.

So this is not merely unused code. It is the version the register records as
wrong, left beside the one that replaced it — and its docstring still opens with
"Usage in daemon:" and three lines of instructions for wiring it up, which is the
worst shape dead code takes: it reads as the way to do the thing. **L7** is about
exactly this, and the index cache removed two days ago was the same shape.

Certainty before deleting, since that was the condition: no import of it anywhere,
static or dynamic; no entry point; nothing in packaging, the systemd units, the
man page, QE or the documentation; and no test covers it. Every module in the
three packages still imports, ruff passes, and the suite is 2893 — unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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