Clean up utils and fw_utils

[laurenyu]

We have two files that are just collections of somewhat-unrelated functions. I think there’s some notion of the functions in fw_utils being used only for frameworks, but utils also contains some functions that are used only for frameworks. It's also generally accepted that a generic name such as "util" makes it easy to keeping adding more unrelated functions into a file/module, causing it to become increasingly harder to maintain.

I’d like to move most of these functions to the following locations:

• the new classes proposed in Refactor sagemaker.session.Session #1463
• the new class proposed in Create a single module for generating image URIs #1464
• some new modules where it makes sense (e.g. one for generating names of SageMaker resources)

In addition, I’d like to deprecate the following functions:

• get_unsupported_framework_version_error: this function is used only by XGBoost, and goes against the original rationale of not wanting to require a Python SDK upgrade just to use a newer framework version. The alternative would be to have all frameworks follow XGBoost's logic.
• to_str: this function was written specifically for Python 2 compatibility, so we won’t need it anymore after Drop Python 2 support #1461
• empty_framework_version_warning: this function is used when customers don’t set framework_version, which will become a required parameter with Require framework_version for framework estimators, models, etc. #1465
• debug: unused as far as I can tell
• generate_tensorboard_url: unused as far as I can tell
• extract_name_from_job_arn: this function’s usage was removed in an earlier PR
• parse_s3_url: this function already has a replacement in s3.py
• unique_name_from_base: this function can go to the test files

[akrishna1995]

Hi @laurenyu - We have added your feature request to our backlog of feature requests and may consider putting it into future SDK versions. I will go ahead and close the issue now, please let me know if you have any more feedback.