I know that in N I didn't always have the notification of which WiFi network my phobe was connected to, but now in Oreo I do. I can't find how to turn it off though!
Your not the only one. I have this useless notification as well. Whenever the phone connects to WiFi, a useless notification pops up in the notifications letting me know that I've connected to the wifi. I already know I connected and I don't need Android telling me that it has connected. I've not found a way to disable it.