@vince.vs
to expand a bit on the answer given, the system allows for applications to add to the predefined user metrics, but there is no provision to remove an existing user metric; not that there is any provision to remove features added to the system by apps, there is no such feature but even if there was one, no app could use it to clean an user metric added to the system because there is no api for that.
If this is really annoying for you the system database for user metrics is /var/lib/usermetrics/usermetrics6.db and I'd guess that (if you know your way with sqlite3 utility) hacking around in this sqlite database could help you to bid good riddance to this user metric and it may even work after restarting the phone, but it's at your risk. I did not try it myself, I don't know if renumbering the entries is necessary or useful or deadly.