EmbeddingBag saving/loading in 'tf' save_model mode

[AlexanderLavelle]

While using TFX recently, it came to my attention that the EmbeddingBag layer does not save correctly in 'tf' format. This is because there is an attribute that is undefined -- in VSCode it can easily be seen as undefined. After some research into this issue, self.input_length should not be be present in EmbeddingBag as it would require a modification to documentation and because it does not appear necessary to use.