This policy throws errors to the console and addresses an issue in Safari that has LONG since been fixed.
The issue was introduced somewhere in 2017 and fixed with Safari 11.1 in march 2018. Removing this drops those browsers into our next policy of 'origin'.
We introduced this in 2015 (T154702) documented at https://wikitech.wikimedia.org/wiki/Analytics/Data_Lake/Traffic/Pageview_hourly#Changes_and_known_problems_since_2015-06-16
The usage was last evaluated in 3 years ago in 2020 in ticket {T248526}
According to https://analytics.wikimedia.org/dashboards/browsers/#all-sites-by-browser/browser-family-and-major-tabular-view Safari below 13 is now not even registering over 0.1% of users.
Safari 11.3 is also the lowest version of Safari to receive Javascript from MediaWiki.
I think the value of having this extra category is not worth it any longer especially as it throws an error in the console that people sometimes ask questions about.