Witness the node tools alone: the controller's lease names no build any more

The controller ended by its unassignment (issue 1126, ADR 0590), so no build is judged by the lease: the lease
witness, its contract and the direct get the witness asked it with are removed, and its tests now prove each rollback
path on the node tools' PING.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

cmd/mesh-host/witnessing.go

@@ -146,9 +146,8 @@ func launcherReplaced(pid int, proc, path string) bool {
 
 // watchWhatThisHostPlaced judges the core builds this host placed, until ctx ends (to-be 45 §8).
 func watchWhatThisHostPlaced(ctx context.Context, node string, queue *link.Session, say func(string)) {
-	host, _ := os.Hostname()
 	w := &witness.Watcher{
-		Root: apply.DaemonRoot(), Node: node, Host: host,
+		Root: apply.DaemonRoot(), Node: node,
 		Asker: func() link.Asker { return queue.Asker() },
 		Run:   witness.Runner(apply.ExecRunner),
 		Hold: func(f func()) {