[Content Improvement] - update deprecated functions

[npichetto-cei]

Link to the notebook
blazingtext_text_classification_dbpedia.ipynb
, presumably others with references to deprecated functions

What aspects of the notebook can be improved?
Update deprecated function calls to use their replacements:

What are your suggestions?

• replace sagemaker.amazon_estimator.get_image_uri() with sagemaker.image_uris.retrieve()