You just can't query by name anymore. You'll have to iterate through all your buffs in a loop and check each of their names until it finds the one you're looking for, by checking their names one by one.
Example from wowpedia:
lua Code:
for i=1,40 do
local name, icon, _, _, _, etime = UnitBuff("player",i)
if name == "Summon Chauffeur" or name == "Ban-Lu, Grandmaster's Companion" then
--do things
end
end
btw:
https://wow.gamepedia.com/Patch_8.0.1/API_changes
Not a complete list, but it has a bunch of stuff.