hive CA: delete ca.pem, ca-previous.pem and ca-key.pem, the bundle is the store's root

The gateway leaf comes from the store's pki mount, so a hive CA's
certificates anchor nothing and its key is a secret outside the store.

- hive-tls-ca writes trust-bundle.pem from swarm-services-root.pem alone;
  the ca.pem and ca-previous.pem slots are gone.
- Every host deletes ca.pem, ca-previous.pem and ca-key.pem in
  deploy.hive-controller.tls.stateDir with tmpfiles `r` rules that follow
  the option. The removal shim, now host-ca-removed.nix, holds these
  beside the /var/lib/swarm-ca rule and the swarm.ca.* removals.
- deploy.bao.clientCaFile, deploy.bao.serverCaFile and
  deploy.swarm-controller.hiveClientCaFile naming /var/lib/swarm-ca or one
  of the deleted hive CA files fail evaluation, naming the store's mTLS CA
  (/var/lib/swarm-bao-pki/ca.pem on the store's host) as the replacement.

module-eval hive-tls covers the single-anchor bundle, the deletion (incl.
a relocated stateDir) and the assertion on all three options.

Refs #4588

docs/swarm/README.md

@@ -34,7 +34,7 @@ grafana, the controller, authelia, …) →
   contract → [`credentials.md`](credentials.md) · how the store comes up,
   who writes its grants and how it unseals → [`bao.md`](bao.md)
 - **swarm CA** — the store root every hive's gateway leaf chains to, and what to
-  hand a peer (`trust-bundle.pem`, never `ca.pem`). → [`ca.md`](ca.md)
+  hand a peer. → [`ca.md`](ca.md)
 - **snapshot store** — the swarm's one `btrfs receive` endpoint,
   `swarm.snapshotStore.{address,port}`. →
   [`snapshot-store.md`](../networking/snapshot-store.md)