Docs: Clean up example files / merge with notebooks

[michaelosthege]

At https://github.com/pymc-devs/pymc3/tree/master/pymc3/examples we have example files that we not updated for years.

for example in /pymc3/examples:
    if example.is_covered_by_notebooks or example_is_irrelevant:
        example.delete()
    else:
        example.refactor_into_notebook()

Related issue #4335

[michaelosthege]

@MarcoGorelli you did the PR on pymc-examples , so naturally you could do this and #4335 as well?
Also how should we proceed with PRs such as #4325 that target the notebooks?

[MarcoGorelli]

I think they should be moved so they target pymc-examples directly

I haven't yet figured out how to build the docs in a way with what's consistent with the website, so have removed my assignment til then

[michaelosthege]

Closing because the files were moved already.