Okay I did some research and I was wrong. There is no confirmation Intel specifically removed the IME from NSA's PCs. It's just that some reverse engineers found a flag that supposedly disables it, and their theory is that it was meant for the NSA.

https://www.notebookcheck.net/Eureka-The-Intel-Management-Engine-can-finally-be-disabled-thanks-to-the-NSA.245922.0.html

I believe this is the switch System76 and Purism turn off, but as I said, since the blob is still there, we can't be sure that switch actually works or if it's just a trap.