I do not think there was an active legion dismantling roads. I like the empire building thing but I do not want City Skylines type of management. Roads built should stay until they decay because of lack of maintenance.
I did once a suggestion about
roads maintenance, where I argued that roads without maintenance will disappear after 50 years. However, this is not what the OP demands. If the player wants to dismantle a road, a legion should be used to do it but it will be quite anachronistic IMHO, maybe someone can prove me wrong.