I assume they removed the riot cheat because it can break your playthrough if you save with it enabled, which people have done since time immemorial.
Since it changed all ped behavior, certain missions become unbeatable and certain things will never trigger.
Most notable example is at the end of Burning Desire, where Denise will never go inside her house at the end of the mission, and instead join the rioting. Problem is that the camera will not yield control back to the player until Denise is inside, and the cheat makes that virtually impossible. Thus, soft-lock.
Once you've saved the game with this cheat enabled, there is no way to disable it except by beating the main story and having the ped behavior overwritten.
It seems like GSG would rather people get mad about less cheats than have R* PR grill them about why tards are @'ing them on twitter and on their website about how their game doesn't work anymore because they can't read the huge warning that tells you NOT to save a game with cheats enabled.