Revert "Selectively initialize SoA types"

[WardBrian]

Submission Checklist

• [x] Run unit tests
• Documentation
  • [ ] If a user-facing facing change was made, the documentation PR is here:
  • [x] OR, no user-facing changes were made

Release notes

Reverted #1323 as https://github.com/stan-dev/math/pull/2978 provides a better solution at a lower level.

Copyright and Licensing

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the BSD 3-clause license (https://opensource.org/licenses/BSD-3-Clause)

[codecov[bot]]

Codecov Report

Merging #1376 (a80ac26) into master (7b69a19) will decrease coverage by 0.01%. Report is 5 commits behind head on master. The diff coverage is 66.66%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1376 +/- ## ========================================== - Coverage 89.93% 89.93% -0.01% ========================================== Files 63 63 Lines 10704 10699 -5 ========================================== - Hits 9627 9622 -5 Misses 1077 1077 ``` | [Files](https://app.codecov.io/gh/stan-dev/stanc3/pull/1376?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev) | Coverage Δ | | |---|---|---| | [src/analysis\_and\_optimization/Optimize.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1376?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL2FuYWx5c2lzX2FuZF9vcHRpbWl6YXRpb24vT3B0aW1pemUubWw=) | `93.23% <66.66%> (-0.07%)` | :arrow_down: |

[WardBrian]

With the new tests added, https://jenkins.flatironinstitute.org/blue/organizations/jenkins/Stan%2FStanc3/detail/PR-1376/2/pipeline/ failed (as expected)

Running again against @SteveBronder's branch from https://github.com/stan-dev/math/pull/2978: https://jenkins.flatironinstitute.org/blue/organizations/jenkins/Stan%2FStanc3/detail/PR-1376/3/pipeline