update comment

rust/src/bin/main.rs

@@ -68,15 +68,14 @@ async fn main() {
         _ =  signal::ctrl_c() => {}
     }
 
-    // The moment the message_handler is dropped, the sender of the request is also dropped,
-    // which means that the state machine shuts itself down.
+    // The moment the message_handler is dropped, the sender half of the request channel is also
+    // dropped, which means that the state machine shuts itself down.
     warn!("shutting down service");
     let _ = state_machine_handle.await;
 
-    // No need to drop the metrics handle in the select macro.
-    // The moment the state machine is dropped, the sender of the metrics is also dropped,
-    // which means that the metric handle is resolved after all remaining messages have been
-    // processed.
+    // The moment the state machine is dropped, the sender half of the metrics channel is also
+    // dropped, which means that the metric handle is resolved after all remaining messages have
+    // been processed.
     warn!("shutting down metrics service");
     let _ = metrics_handle.await;
 }