Use head state for exit verification

Author: paulhauner

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -2173,12 +2173,13 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         &self,
         exit: SignedVoluntaryExit,
     ) -> Result<ObservationOutcome<SignedVoluntaryExit, T::EthSpec>, Error> {
-        // NOTE: this could be more efficient if it avoided cloning the head state
-        let wall_clock_state = self.wall_clock_state()?;
+        let head_snapshot = self.head().snapshot;
+        let head_state = &head_snapshot.beacon_state;
+
         Ok(self
             .observed_voluntary_exits
             .lock()
-            .verify_and_observe(exit, &wall_clock_state, &self.spec)
+            .verify_and_observe(exit, head_state, &self.spec)
             .map(|exit| {
                 // this method is called for both API and gossip exits, so this covers all exit events
                 if let Some(event_handler) = self.event_handler.as_ref() {