[Q] Can't Remove SuperSU topic

I wanted to get my Verizon M8 on 4.4.2 back to stock, and I found and followed this guide.

1. Flashed RUU


2. Relocked Bootloader


3. S-On

I got through everything successfully, except I can't get SuperSU permanently removed now. The in-app remove thing doesn't work and the Universal Unroot app didn't work. I Googled furiously and found things like this (part 2) and this, but nothing is working.

Is there anything else I can try?