Stan 2.34: Remove deprecated code paths following 2.33 removals

[WardBrian]

Submission Checklist

• [x] Run unit tests
• Documentation
  • [ ] If a user-facing facing change was made, the documentation PR is here:

Release notes

• The compiler no longer recognizes language constructs removed in 2.33. This primarily affects the canonicalizer.
• The deprecated implicit conversion of reals to boolean conditions has been removed.

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 #1388 (21fac2a) into master (e464f6a) will decrease coverage by 0.06%. The diff coverage is 85.71%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1388 +/- ## ========================================== - Coverage 89.93% 89.88% -0.06% ========================================== Files 63 63 Lines 10707 10505 -202 ========================================== - Hits 9629 9442 -187 + Misses 1078 1063 -15 ``` | [Files](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev) | Coverage Δ | | |---|---|---| | [src/frontend/Pretty\_printing.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL2Zyb250ZW5kL1ByZXR0eV9wcmludGluZy5tbA==) | `92.01% <ø> (+0.55%)` | :arrow_up: | | [src/middle/Stan\_math\_signatures.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL21pZGRsZS9TdGFuX21hdGhfc2lnbmF0dXJlcy5tbA==) | `98.01% <100.00%> (-0.14%)` | :arrow_down: | | [src/middle/Utils.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL21pZGRsZS9VdGlscy5tbA==) | `88.09% <100.00%> (-1.71%)` | :arrow_down: | | [src/stan\_math\_backend/Lower\_expr.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL3N0YW5fbWF0aF9iYWNrZW5kL0xvd2VyX2V4cHIubWw=) | `93.15% <100.00%> (+0.26%)` | :arrow_up: | | [src/stanc/stanc.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL3N0YW5jL3N0YW5jLm1s) | `82.14% <ø> (-0.13%)` | :arrow_down: | | [src/frontend/Ast.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL2Zyb250ZW5kL0FzdC5tbA==) | `68.77% <66.66%> (+0.07%)` | :arrow_up: | | [src/frontend/Ast\_to\_Mir.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL2Zyb250ZW5kL0FzdF90b19NaXIubWw=) | `94.58% <83.33%> (+0.57%)` | :arrow_up: | | [src/frontend/Deprecation\_removals.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL2Zyb250ZW5kL0RlcHJlY2F0aW9uX3JlbW92YWxzLm1s) | `75.00% <88.88%> (-15.70%)` | :arrow_down: | | [src/frontend/Typechecker.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL2Zyb250ZW5kL1R5cGVjaGVja2VyLm1s) | `91.97% <88.88%> (+0.48%)` | :arrow_up: | | [src/frontend/Deprecation\_analysis.ml](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev#diff-c3JjL2Zyb250ZW5kL0RlcHJlY2F0aW9uX2FuYWx5c2lzLm1s) | `82.00% <75.00%> (-6.12%)` | :arrow_down: | | ... and [1 more](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev) | | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/stan-dev/stanc3/pull/1388/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev)