They removed the Interface-option and its associated cVar as far as I can tell, but you can hide it with this:
local f = CreateFrame("Frame", nil, UIParent)
f:SetScript("OnEvent", function(self, event, name)
if name == "Blizzard_TimeManager" then
You have to register for ADDON_LOADED since TimeManagerClockButton doesn't exist until Blizzard_TimeManager is loaded.