Get the older iris code examples working

[pp-mo]

Requested by @hdyson Content in question is in https://github.com/scitools-classroom notably https://github.com/scitools-classroom/iris_example_code : which is so old it is Python 2 code

My guess was that we only maintain https://github.com/scitools-classroom/courses But others have disagreed. Personally, I do nevertheless think there is an opportunity to review this content, and maybe retire some of it.

[hdyson]

Given the scitools classroom is referenced from the iris user guide, I think this does imply some level of curation for the tutorials. My personal opinion is that a small number of curated examples is better than a larger number of examples in various states of obsolesence.

[ESadek-MO]

@SciTools/peloton

The decision seems to be whether we update all existing repositories, or if we limit what the user guide links to. Each one needs to be considered individually on its merits. There a couple which I think are givens, such as courses and mesh-tutorial, and the rest would require thought/discussion.

I think the way forward for this would be for someone to scope the amount of work needing, and the contents, for easier team discussion.