Remove Julian date support

[oscargus]

PR summary

PR checklist

• [N/A] "closes #0000" is in the body of the PR description to link the related issue
• [N/A] new and changed code is tested
• [N/A] Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• [N/A] Documentation complies with general and docstring guidelines

[tacaswell]

#26849 should fix azure, merging over the failure.

I am curious about why John added this to begin with (they came in in 2006!).

[WeatherGod]

John had a background in Perl, and Julian calendar support is pretty complete in it. Also, Julian day is a bit special because it uses the international date line (180 degrees longitude) instead of the prime meridian as its delimiter for days. This helps with grouping international data by common days, which I'd imagine is useful for people in finance, which John was also involved in for his job.

[jklymak]

We maybe could consider ammending the change note to indicate the conversion from our num to Julian days. It's a straightforward offset.