[tf.data] Minor tweaks to legacy `ModelDatasetOp` implementation.
[tf.data] Minor tweaks to legacy `ModelDatasetOp` implementation.

This CL removes some unused code and also changes the implementation of `ModelDatasetOp::Dataset::Iterator` to avoid overriding the `model` parameters of `IteratorContext`.

PiperOrigin-RevId: 372988027
Change-Id: I107d0fcfdc22f399038a83522faf4c83f0be50d8

karllessard/tensorflow,yongtang/tensorflow,Intel-tensorflow/tensorflow,sarvex/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,gautam1858/tensorflow,karllessard/tensorflow,Intel-tensorflow/tensorflow,Intel-tensorflow/tensorflow,frreiss/tensorflow-fred,frreiss/tensorflow-fred,tensorflow/tensorflow-pywrap_tf_optimizer,Intel-Corporation/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow,yongtang/tensorflow,frreiss/tensorflow-fred,paolodedios/tensorflow,tensorflow/tensorflow,gautam1858/tensorflow,sarvex/tensorflow,Intel-Corporation/tensorflow,Intel-Corporation/tensorflow,Intel-tensorflow/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_saved_model,karllessard/tensorflow,gautam1858/tensorflow,paolodedios/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow,karllessard/tensorflow,karllessard/tensorflow,yongtang/tensorflow,yongtang/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_saved_model,karllessard/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-experimental_link_static_libraries_once,karllessard/tensorflow,tensorflow/tensorflow-pywrap_saved_model,gautam1858/tensorflow,gautam1858/tensorflow,karllessard/tensorflow,yongtang/tensorflow,sarvex/tensorflow,tensorflow/tensorflow,yongtang/tensorflow,gautam1858/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow,frreiss/tensorflow-fred,frreiss/tensorflow-fred,yongtang/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,frreiss/tensorflow-fred,paolodedios/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,frreiss/tensorflow-fred,Intel-tensorflow/tensorflow,paolodedios/tensorflow,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-Corporation/tensorflow,karllessard/tensorflow,gautam1858/tensorflow,frreiss/tensorflow-fred,karllessard/tensorflow,sarvex/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-tensorflow/tensorflow,paolodedios/tensorflow,frreiss/tensorflow-fred,paolodedios/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,Intel-Corporation/tensorflow,Intel-Corporation/tensorflow,tensorflow/tensorflow-pywrap_saved_model,yongtang/tensorflow,paolodedios/tensorflow,Intel-Corporation/tensorflow,Intel-tensorflow/tensorflow,yongtang/tensorflow,karllessard/tensorflow,tensorflow/tensorflow-pywrap_saved_model,Intel-Corporation/tensorflow,yongtang/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,sarvex/tensorflow,frreiss/tensorflow-fred,gautam1858/tensorflow,sarvex/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,frreiss/tensorflow-fred,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-experimental_link_static_libraries_once,sarvex/tensorflow,yongtang/tensorflow,Intel-tensorflow/tensorflow,paolodedios/tensorflow,sarvex/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_tf_optimizer,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-experimental_link_static_libraries_once,paolodedios/tensorflow,gautam1858/tensorflow