Several cleanups:
Several cleanups:

renamed RecordBasedTFXIO.RawRecordBeamSourceInternal to _RawRecordBeamSourceInternal (it's a "protected" interface)
similarily, RawRecordToRecordBatchInternal -> _RawRecordToRecordBatchInternal

removed TFExampleRecord._SerializedExamplesSource (it's essentially _RawRecordBeamSourceInternal).

PiperOrigin-RevId: 313628755

tensorflow/transform