There are commits from 2009-05-02 calculating indent_level but not
using it to indent. There are some other commits from 2011-02-22
commenting out the code with the message "it does not work". Nobody cared
enough about it for 10 years, time to remove commented code and leftovers.

Linked PRs

• gh-95382: Improve performance of json encoder with indent #118105
• gh-95382: Use cache for indentations in the JSON encoder #118636