NT SERVICE\SQLTELEMETRY User
This login is used for Extended Events. More information here: Extended Events logins

I disabled it once, and I was no longer able to collect the data I needed. If I were you I'd keep the login as it is, unless of course you already know that you wont need tracing/Extended Events.

When it comes to telemetry you may like to read the instructions how it can be disabled: Disable telemetry Apparently many users are not happy about telemetry. More information here