node: drop stale dead-code allows and a redundant clock read

Remove the now-stale `#[allow(dead_code)]` on `advance_peer_machine`
and `execute_peer_actions`; both are live (called from the link-dead
reap, rekey cadence routing, and the handshake establish sites).

In `route_rekey_cadence`, reuse the ambient context timestamp for the
machine step instead of taking a second clock sample; the extra
sample's only consumer was the currently-inert cutover drain timer, so
the change is behavior-neutral.

src/node/dataplane/peer_actions.rs

@@ -75,7 +75,6 @@ impl Node {
     /// `index_allocator` are **distinct `Node` fields**, so the collect below is
     /// a disjoint two-field borrow the checker accepts; once the actions are
     /// collected both borrows drop and the executor runs against `&mut self`.
-    #[allow(dead_code)]
     pub(in crate::node) async fn advance_peer_machine(
         &mut self,
         link: LinkId,
@@ -100,7 +99,6 @@ impl Node {
     /// single flat future (no boxing) and the emitted order is preserved (the
     /// establish sequences always end in `PromoteToActive`, so its follow-ups run
     /// after any siblings).
-    #[allow(dead_code)]
     pub(in crate::node) async fn execute_peer_actions(
         &mut self,
         link: LinkId,

src/node/handlers/rekey.rs

@@ -117,7 +117,7 @@ impl Node {
         self.advance_peer_machine(
             link,
             PeerEvent::RekeyConsume { action },
-            Self::now_ms(),
+            ambient.now_ms,
             &ambient,
         )
         .await;