This is a REALLY old feature that was made for skateboards back around like 2010.
For some reason, calling the UnbindButton function causes Roblox to crash. This is probably an oversight caused by changes to the UI over the years, but whatever the reason, running this script crashes Roblox:
local crash = Instance.new("HumanoidController")
crash:BindButton(Enum.Button.Jump,"lol")
crash:UnbindButton(Enum.Button.Jump) -- NULL POINTER!