MNT: Remove Python 2 leftovers

[StefRe]

to improve readability and unify coding style (older code used %, newer contributions use format etc). Modifications were done using pyupgrade.

Files in tinybuild\examples\future were deliberately left unchanged.

I know it's a lot of changed files but I think it greatly improves readability and the Python docs also recommend the use of format over %.

[larsoner]

and the Python docs also recommend the use of format over %.

I actually prefer f-strings nowadays. Is it simple to change to that?

[StefRe]

Is it simple to change to that?

I think so, using the --py36-plus option (which will also change some other things but these changes can be reverted if they occur).

See also the note in the linked docs which sounds good:

pyupgrade is intentionally timid and will not create an f-string if it would make the expression longer or if the substitution parameters are sufficiently complicated (as this can decrease readability).

I'm going to do the f-strings in a separate commit so you can have a look.

[StefRe]

After rebasing I get two failing tests that pass locally so I assume it's not a real test failure. I can't "Rerun failed jobs" in https://dev.azure.com/sphinx-gallery/sphinx-gallery/_build/results?buildId=1246&view=results due to TF400813: The user '7dbe823d-48de-6791-9031-8f872678a096' is not authorized to access this resource. What should I do i such a case? Force push a dummy commit to retrigger the pipeline or is there something more intelligent?

[larsoner]

I usually git commit --allow-empty -m 'TST: Ping' or something, yeah. (Arguably slightly cleaner than a force push.) But I do have permissions as an admin so I'll restart for you now :)

[larsoner]

Thanks @StefRe !