[BUG] Stale sundials library #80
Description
The main Torsten repo has two bundled libraries for sundials:
$ git -C Torsten ls-tree v0.91.2:cmdstan/stan/lib/stan_math/lib | grep sundials_
040000 tree 772f0fcd46bdb81880f3bdc395ee80823e1990ec sundials_5.7.0
040000 tree ac77d81aeb473265f1f001b439e7c1904ab21a60 sundials_6.1.1
stan-dev/maths f9a2f50ef3 (upgrading to sundials v6.0.0; removing old sundials library, 2021-12-18) deleted sundials_5.7.0 when updating to sundials 6.0.0.
When metrumresearchgroup/math merged f9a2f50ef3 to torsten-develop in
f34e458c5c (Merge branch 'master' into torsten-develop, 2022-05-17), the sundials_5.7.0 deletion was not propagated.
I'm not aware of any functional problems caused this extra library. I'm just flagging this as something to consider cleaning up whenever there are other changes to release.