Fix build warnings

Author: jkczyz

lightning-rapid-gossip-sync/src/lib.rs

@@ -271,6 +271,7 @@ pub mod bench {
 					println!("{}", error_string);
 					return;
 				}
+				#[cfg(require_route_graph_test)]
 				panic!("{}", error_string);
 			}
 			assert!(sync_result.is_ok())

lightning/src/routing/network_graph.rs

@@ -2385,7 +2385,7 @@ mod tests {
 
 	#[test]
 	fn network_graph_tlv_serialization() {
-		let mut network_graph = create_network_graph();
+		let network_graph = create_network_graph();
 		network_graph.set_last_rapid_gossip_sync_timestamp(42);
 
 		let mut w = test_utils::TestVecWriter(Vec::new());