fix: drop session span at end of the session (#9126)

codex-rs/otel/src/lib.rs

@@ -17,7 +17,6 @@ use codex_protocol::ThreadId;
 use serde::Serialize;
 use std::time::Duration;
 use strum_macros::Display;
-use tracing::Span;
 
 #[derive(Debug, Clone, Serialize, Display)]
 #[serde(rename_all = "snake_case")]
@@ -42,7 +41,6 @@ pub struct OtelEventMetadata {
 #[derive(Debug, Clone)]
 pub struct OtelManager {
     pub(crate) metadata: OtelEventMetadata,
-    pub(crate) session_span: Span,
     pub(crate) metrics: Option<MetricsClient>,
     pub(crate) metrics_use_metadata_tags: bool,
 }