I was told by TracFone Wireless that this update is not from Android or from Google or from TracFone Wireless, but from Samsung itself, and that it was legitimate. Even so, I did want not want to install any updates on my phone and yet I could not get rid of this stupid notification on the screen which Allowed no option for rejecting me update or closing. 
I had the same problem, using a Samsung Galaxy J-3 with the TracFone service as my carrier. Apparently, it's the problem can be solved by blocking push notifications from Samsung updates or anything that looks similar to Samsung updates, In the system preferences under notifications. Even if you have the notification message on your screen and cannot get rid of it in order to reject the update, if you first block all notifications from Samsung, and then reboot your phone, apparently that notification message goes away, and the update does not install. So far, this is the solution for me but, knock on wood, tomorrow something new could develop, I suppose.