[docs] remove references to recently deleted classes in non-en docs (onnx, feature processors) (#41286)

remove references to old classes

Author: gante

docs/source/es/_toctree.yml

@@ -64,8 +64,6 @@
     title: Entrenador
   - local: sagemaker
     title: Ejecutar el entrenamiento en Amazon SageMaker
-  - local: serialization
-    title: Exportar a ONNX
   - local: torchscript
     title: Exportar a TorchScript
   - local: community