Remove Python 3.8 support

[mrmundt]

Fixes NA

Summary/Motivation:

Remove Python 3.8 support because it is EOL.

Changes proposed in this PR:

• Remove all references to 3.8 in tests and docs
• Remove code that was necessary for pre-3.8 reasons

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[jsiirola]

You are removing necessary documentation that has nothing to do with Python 3.8 compatibility. These overloads are for helping out with IDE auto-completion / documentation and should not be removed.