chore: remove old (bugfix/migration) code

[minisbett]

Describe your changes

Removed various code that is either already old and commented out for a long time or presented updates for very old bancho.py times (e.g. when the country code wasn't saved yet) to clean up the codebase a bit.

Related Issues / Projects

Checklist

• [X] I've manually tested my code
• [X] The changes pass pre-commit checks (make lint)
• [X] The changes follow coding style

[cmyui]

i generally think prs removing backwards compatibilities are tricky to merge, it's kinda risky for low reward

[cmyui]

given they're pretty minor but can result in some pretty bad states i think i'm more comfortable leaving these for now.

i think i would be open to accepting a well tested script to backfill the data issues, at which point i would be willing to remove the jit data fixes here