matrix: drop the per-hive appservice and its unused token

Every hive's homeserver loaded a per-hive `hyperhive` appservice
registration, and the swarm minted and delivered an as_token for it
through bao. No client presented that token: swarm-controller creates
every `@hive-<hive>` sender and every agent account with the swarm
appservice token (hive_sender.rs, agent_token.rs), and no Rust code read
the per-hive one.

Removed, with everything that existed only to serve it:
- hive-matrix.nix: the `hyperhive` registration, its activation-time
  render, the host bind mount of /var/lib/hyperhive/matrix-appservice,
  its LoadCredential entry, and the internal options
  `deploy.matrix.appserviceTokenFile` / `appserviceRegistrationScript`.
  tuwunel now loads only the swarm registration.
- glue-matrix-bao-token.nix and its `swarm-bao-matrix-token` unit.
- glue-bao-tls.nix: the matrix-token leaf and its defaults.
- swarm-bao.nix: the `swarm-matrix-token-<hive>` roles and policies
  (`swarm-bao-matrix-token-policy`), and the options
  `deploy.bao.matrixTokenClient{Cert,Key}File` and
  `matrixTokenCommonNamePrefix`, now mkRemovedOptionModule.
- swarm-secret-publisher.nix: the per-hive token mint and its state dir.
- swarm.nix: the reserved `<matrixTokenCommonNamePrefix>-<hive>` CN.
- swarm-secret-client: `matrix::appservice_token_path`.

The swarm registration (swarm-matrix-ctl, swarm-controller) is untouched.
Comments and docs that pointed at the removed glue file now point at
glue-queue-agent-credential.nix, which has the same reader shape.

Refs #4428

nix/module-eval/bao-basics.nix

@@ -162,13 +162,6 @@ let
       name = "an operator's own certificate path beats the glue's default";
       ok = baoExplicitCerts.services.hyperhive.deploy.bao.serverCertFile == "/etc/pki/bao.pem";
     }
-    {
-      # Absence arm. A store with nothing to serve renders no reader, so the
-      # unit is a function of the PAIRING rather than of the store — which is
-      # the property that makes it glue instead of a feature of either side.
-      name = "a store with no homeserver beside it renders no token reader";
-      ok = !(baoPkcs11.systemd.services ? swarm-bao-matrix-token);
-    }
     {
       # The name a reader dials has to resolve where the store runs; a
       # multi-host swarm resolves it upstream instead.