I had SPRecovery installed.
I had the master FRG22D at the root.
I booted into recovery and:
Wiped cache partition
Wiped data/factory reset
Choose -> Install
Allow update.zip Installation
Install /sdcard/update.zip (deprecated)
Bypassed activation screen
Used ADB to install a file manager (AndExplorer)
Browsed the system folders, found nothing but stock apps.
Nothing leftover, nothing in the apps drawer.
Totally clean, 100% stock.
Obviously the /system partition is completely wiped when applying the master file. There should be no traces of superuser or other root utilities.