DEPR:  ‘AS’, ‘BA’ and ‘BAS’ in favour of ‘YS’, ‘BY’ and ‘BYS’
xref #55252
- deprecated strings ‘AS’, ‘BA’ and ‘BAS’ in favour of ‘YS’, ‘BY’ and ‘BYS’.
-  deprecated annual frequencies with various fiscal business year ends: “BA-DEC", “BA-JAN", etc. in favour of “BY-DEC", “BY-JAN", etc.
- deprecated annual frequencies with various fiscal year begin: “AS-DEC", “AS-JAN", etc. in favour of “YS-DEC", “YS-JAN", etc.

> Nice!
> 
> I think this is just missing a 2.2.0 whatsnew note?
> 
> OK to add it in the next PR though, happy to get this in before conflicts creep in 😄

yes, it would be great if we can get it in. I will add the note to 2.2.0 whatsnew in my next PR.