refactor: remove the unnecessary Option in the z_liveliness example…

… for clarity (eclipse-zenoh#1316)

examples/examples/z_liveliness.rs

@@ -26,16 +26,14 @@ async fn main() {
     let session = zenoh::open(config).await.unwrap();
 
     println!("Declaring LivelinessToken on '{}'...", &key_expr);
-    let mut token = Some(session.liveliness().declare_token(&key_expr).await.unwrap());
+    let token = session.liveliness().declare_token(&key_expr).await.unwrap();
 
     println!("Press CTRL-C to undeclare LivelinessToken and quit...");
     std::thread::park();
+
     // LivelinessTokens are automatically closed when dropped
     // Use the code below to manually undeclare it if needed
-    if let Some(token) = token.take() {
-        println!("Undeclaring LivelinessToken...");
-        token.undeclare().await.unwrap();
-    };
+    token.undeclare().await.unwrap();
 }
 
 #[derive(clap::Parser, Clone, PartialEq, Eq, Hash, Debug)]