Fix new unused variable warning in test_utils.rs

Author: TheBlueMatt

lightning/src/util/test_utils.rs

@@ -423,7 +423,7 @@ impl<Signer: sign::WriteableEcdsaChannelSigner> chainmonitor::Persist<Signer> fo
 		chain::ChannelMonitorUpdateStatus::Completed
 	}
 
-	fn update_persisted_channel(&self, funding_txo: OutPoint, update: Option<&channelmonitor::ChannelMonitorUpdate>, _data: &channelmonitor::ChannelMonitor<Signer>, update_id: MonitorUpdateId) -> chain::ChannelMonitorUpdateStatus {
+	fn update_persisted_channel(&self, funding_txo: OutPoint, _update: Option<&channelmonitor::ChannelMonitorUpdate>, _data: &channelmonitor::ChannelMonitor<Signer>, update_id: MonitorUpdateId) -> chain::ChannelMonitorUpdateStatus {
 		let mut ret = chain::ChannelMonitorUpdateStatus::Completed;
 		if let Some(update_ret) = self.update_rets.lock().unwrap().pop_front() {
 			ret = update_ret;