What will actually go away tomorrow besides the season pass/challenges?

I saw a Twitter post from the Bungie account, saying that you should remember to claim any episode engrams. Like, what? They go away?? So basically asking; what else is going away, or Just engrams specifically? And I’m asking as a multi-year veteran. This still is still confusing. I know I will still be able to play the activities and gain engrams but, like anything think Flakes and such will go away too?