Expire deprecations from 3.6

[oscargus]

PR Summary

Not all, but most (all?) of the ones I understood (quite) easily...

Split into multiple commits for somewhat sensible commit messages. Will add an api-change note.

The first commit also improves the argument checking of (set_)pickradius slightly.

PR Checklist

Documentation and Tests

• Has pytest style unit tests (and pytest passes)
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• New plotting related features are documented with examples.

Release Notes

• New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst

[oscargus]

One would have expected this to warn earlier?

Edit: it did warn, but it seems like the doc-build didn't pick it up.

[efiring]

Thank you for doing this. I read through the file diffs without finding any problems. I did not try to match every removal with a note in the changes/removals file, but I did notice that removals from the backends don't seem to be mentioned there.

[oscargus]

Ahh, you are correct. Well spotted!

In the 3.6 documents it was a big list of all the backend changes, but I didn't touch the interactive ones, so at the time I just skipped that for later and forgot about it...

[oscargus]

This is now added.

Note that some of the things didn't have deprecation notices in the 3.6 docs, such as positional argument renaming.

[oscargus]

Thanks @anntzer ! Should be sorted out now.

[anntzer]

postci

[ksunden]

Only hard blocker is the offsetbox kw-only arg position, but also commented on collections version of pickradius if you wish to make that consistent with some other pickradus implementations

[oscargus]

Thanks @ksunden ! Good finds!