Update proceedings links for new proceedings site

[fwkoch]

This updates proceedings links across the site:

• For links like https://conference.scipy.org/proceedings/scipy<year>, I updated to https://proceedings.scipy.org/<year>
• For all the aws redirects on proceedings index and individual paper pages, I updated the redirects to https://doi.org/<doi> (which now point to proceedings.scipy.org)

While creating this PR I also confirmed that all the new links exist and correctly resolve to the new Curvenote proceedings site.

Note - I did not re-build the static site after these changes; this was mostly an automated find-and-replace job. Happy to make changes if there is something here that does not work with the static site build!

[achabotl]

I think this should work. Thank you all for you hard work bringing the proceedings onto Curvenote and for not breaking the web. :D