chore: remove campo is_using_sse nao usado do ChatPollerHandle

O campo estava duplicado - ChatRuntime ja tem seu proprio is_using_sse.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/desktop/src-tauri/src/chat.rs

@@ -418,7 +418,6 @@ struct SseUpdateEvent {
 struct ChatPollerHandle {
     stop_flag: Arc<AtomicBool>,
     join_handle: JoinHandle<()>,
-    is_using_sse: Arc<AtomicBool>,
 }
 
 impl ChatPollerHandle {
@@ -545,7 +544,6 @@ impl ChatRuntime {
         *guard = Some(ChatPollerHandle {
             stop_flag,
             join_handle,
-            is_using_sse: self.is_using_sse.clone(),
         });
 
         Ok(())