See https://gerrit.wikimedia.org/r/1149395 for a list of counters that are related to the feature. As far as can tell the WMDE-TechWish team started working on this but never fully implemented it, see https://meta.wikimedia.org/wiki/WMDE_Technical_Wishes/Watchlist_Expiry. That was later done by the Community-Tech team, see https://meta.wikimedia.org/wiki/Community_Tech/Watchlist_Expiry.

For reference: There is a whole bunch of WatchedItemStore… counters in the class with the same name. The code is still used, but the counters are probably not. Dear Community-Tech, please check if you still need any of this.

The patch also removes a rollbackconfirmation… counter, related to the Confirmation prompt for rollback action project that was finished in 2019, see https://meta.wikimedia.org/wiki/WMDE_Technical_Wishes/Rollback.