Hey, It happens quite often that people add a temporary config variable to the code and then mediawiki-config repo, they remove it from code and forget to remove the config in mediawiki-config. My quick check found these config variables to be unused:
$wgSpamBlacklistEventLogging $wgUseContributionTracking $wgMFLazyLoadReferences $wgMFExperiments $wgDepictsQualifierProperties $wgMediaInfoEnableOtherStatements $wgGEHelpPanelSearchEnabled $wgDisableRollbackConfirmationFeature $wgCirrusSearchEnableSearchLogging
Unused config variables are bad because they make our overly large config file even bigger (IS.php is already over 20k lines) and it can be confusing (like https://phabricator.wikimedia.org/T225183). I will add more unused config variables to the list by improving the search but please check and remove them if you introduced any of the aforementioned variables.
Thanks Best
wikitech-l@lists.wikimedia.org