tidy up overly an verbose string conversion

Author: dwrensha

capnp-rpc/examples/pubsub/server.rs

@@ -167,8 +167,7 @@ pub async fn main() -> Result<(), Box<dyn std::error::Error>> {
                             subscriber.requests_in_flight += 1;
                             let mut request = subscriber.client.push_message_request();
                             request.get().set_message(
-                                (&format!("system time is: {:?}", ::std::time::SystemTime::now())
-                                    [..])
+                                format!("system time is: {:?}", ::std::time::SystemTime::now())[..]
                                     .into(),
                             )?;
                             let subscribers2 = subscribers1.clone();