Remove all the PY2 compat code

[Valinor]

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See #8566

• [X] Title is descriptive/clear for inclusion in release notes.
• [ ] Applied a Component: xxx label.
• [ ] Applied the api-deprecation or api-break label.
• [ ] Applied the release-highlight label to be highlighted in release notes.
• [ ] Added to the milestone version it was merged into.
• [ ] Unittests are included in PR.
• [ ] Properly documented, including versionadded, versionchanged as needed.

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[Valinor]

Hi @Valinor !

I've left some minor suggestions.

Nice work and cleanup 🧹 BTW!

Thanks for the review. Shame on me to let pass all of these :').

I will try to understand why some tests fails on the ci, and not for me, and take care of your suggestions.

[misl6]

I will try to understand why some tests fails on the ci

When you push changes, make sure to rebase on top of latest master, as the CI errors you seen might be related to https://github.com/kivy/kivy/pull/8618 (so, not your fault)

[misl6]

@Valinor FYI:

We also may want to do some cleanup here: https://github.com/kivy/kivy/blob/dc7fd3d8ae28029ebecfbb923af37caa4a5245c9/kivy/uix/screenmanager.py#L1090

[misl6]

Hi @Valinor,

This is a friendly ping, are you still active on this PR?

[misl6]

@Valinor FYI: I've performed some changes to your PR due to inactivity, thank you for doing most of the work BTW!

[welcome[bot]]

Congrats on merging your first pull request! 🎉🎉🎉

[Valinor]

@Valinor FYI: I've performed some changes to your PR due to inactivity, thank you for doing most of the work BTW!

Thanks, and sorry for my inactivity. I will try to be more productive next time. Great change, thanks for your work.