fix: remove unused warn import

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-relay/src/main.rs

@@ -9,7 +9,7 @@ use std::sync::Arc;
 use std::time::Duration;
 
 use tokio::sync::Mutex;
-use tracing::{error, info, warn};
+use tracing::{error, info};
 
 use wzp_proto::MediaTransport;
 use wzp_relay::config::RelayConfig;