chore: drop unreachable pre Python 3.9 md5 fallback in hash

[Andrej730]

Hello. Removing fallback for Python <3.9 missing usedforsecurity option in hashlib.md5.
Since project is targeting Python >= 3.10, this code is dead and can be safely removed.

aws-sam-cli/pyproject.toml

Line 10 in 9101836

requires-python = ">=3.10"

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