Remove redundant contextMenu disposal in TrayIcon

The explicit disposal of contextMenu in TrayIcon's dispose method has been removed, likely because contextMenu is now managed elsewhere or its disposal is handled automatically.

Author: lijy91

packages/nativeapi/lib/src/tray_icon.dart

@@ -254,9 +254,6 @@ class TrayIcon
     // Dispose event emitter (will call stopEventListening if needed)
     disposeEventEmitter();
 
-    if (contextMenu != null) {
-      contextMenu!.dispose();
-    }
     bindings.native_tray_icon_destroy(_nativeHandle);
   }
 }