Yep, my 4S keeps prompting me to update to iOS 8.4.1 as well. The bad part is that aside from resetting it, there isn't a way to remove the downloaded iOS update hogging a couple GB of space. Bad move on Apple's part. I think iOS 7.2 was the first to allow you to remove downloaded updates, though they usually come back anyway.
I could just jailbreak it and then use a Cydia tweak to remove the OTA and keep it off but then I couldn't easily reset it. Though it may be worth JB'ing to use Odysseus OTA and get it up to 6.1.3 from 6.1.0. But that's the only reason I would.
For now though, I'm selling my iPhone 7 and using the 4S I bought full-time. Reason being the reception has driven me bonkers today. No signal, 1 bar, none again, message send failure, sent as SMS failure, etc. Stuck my SIM in the 4S and I've been sending SMS and iMessages all day!
I may look into getting the BlackBerry KEYone actually. But until then, it's back to iOS 6 for me. And I personally love it! I'll miss some apps but nothing critical. I've got my music, phone, sms, calendar (Google), notes, find my friends, flashlight, radar app, weather apps, bible app, Dropbox, Google drive, Google maps, etc all working just fine.
I also snagged a Speck CandyShell case in red for a whole $3 shipped on eBay. Arrived brand new unopened and genuine from what I can tell! Score!