Remove more outdated code for v1.0

[jgabry]

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

Remove more outdated code in preparation for v1.0 and convert save_metric and save_cmdstan_config to global options

Copyright and Licensing

Please list the copyright holder for the work you are submitting
(this will be you or your assignee, such as a university or company):
Jonah Gabry

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.85%. Comparing base (962dd83) to head (d2fa15e).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1159      +/-   ##
==========================================
+ Coverage   90.64%   90.85%   +0.21%     
==========================================
  Files          14       14              
  Lines        5934     5908      -26     
==========================================
- Hits         5379     5368      -11     
+ Misses        555      540      -15     

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