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/matrix-core.nix

@@ -59,14 +59,7 @@ let
         lib.hasInfix "client_max_body_size 100048576;" c && !(lib.hasInfix "client_max_body_size 50M" c);
     }
     {
-      # Absence arm for the one above, and the reason the gate is the identity
-      # rather than the homeserver: without it, deploying matrix anywhere would
-      # render a reader that cannot authenticate.
-      name = "a homeserver with no way to authenticate to the store renders no token reader";
-      ok = !(matrixNoBaoIdentity.systemd.services ? swarm-bao-matrix-token);
-    }
-    {
-      # Absence arm for the case above. A hive with no client identity gets no
+      # Absence arm. A hive with no client identity gets no
       # store environment at all — the daemon reports a queue it cannot serve
       # rather than a handshake it cannot explain.
       name = "a hive with no client identity gives hive-c0re no store environment";