Don't try to inline StanLib fun calls, ever

[WardBrian]

Closes #1473. As far as I can tell, this code was always wrong, but relied on the map lookup failing for StanLib functions. How this got missed during the function overloading PRs I'm not sure.

Submission Checklist

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

Release notes

Fixed a internal compiler error in the function inlining optimization

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]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 89.67%. Comparing base (8d74ceb) to head (3b73657).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/analysis_and_optimization/Optimize.ml	93.33%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1474   +/-   ##
=======================================
  Coverage   89.67%   89.67%           
=======================================
  Files          63       63           
  Lines       10656    10656           
=======================================
  Hits         9556     9556           
  Misses       1100     1100           

Files with missing lines	Coverage Δ
src/analysis_and_optimization/Optimize.ml	92.32% <93.33%> (ø)