@mmatej: It *should* remove the jailbreak update key (pubdevkey01.pem), but not the kindlet keystore

.
I never tried it, so I'm not sure why yifan's package didn't seem to do anything, but it should have removed the updater key. The only potential issues I see with it is that it won't run on some European 3G Touch, the target OTA is a bit low (but still high enough), and it relies on legacy helper functions for progress handling, but none of that should prevent it from removing a single puny file

. [Unless the updater system does some black magic in the background with its public keys...]