Remove leftover Python 2 references

[timlehr]

Summarize your change.

Removing some leftover Python 2 references in setup.py

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (1812f06) 90.15% compared to head (5e6ce71) 90.15%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #19 +/- ## ======================================= Coverage 90.15% 90.15% ======================================= Files 3 3 Lines 1107 1107 ======================================= Hits 998 998 Misses 109 109 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `90.15% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenTimelineIO#carryforward-flags-in-the-pull-request-comment) to find out more.

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[timlehr]

@apetrynet Not sure about the new Python versions. Which one do we support officially? CI seems to run 3.7-3.10

[apetrynet]

I don't know ATM. But adding the ones run in the ci should suffice. At least it's 1 to 1

[timlehr]

I think those are all present already.

[apetrynet]

Ah, sorry I was unclear. I meant in the versions listed in setup.py

[timlehr]

3.7 - 3.10 are already listed: https://github.com/OpenTimelineIO/otio-aaf-adapter/pull/19/files#diff-60f61ab7a8d1910d86d9fda2261620314edcae5894d5aaa236b821c7256badd7R54-R58

[apetrynet]

Sorry, @timlehr I should have expanded the diff 🤦‍♂️