The antiphon Exsúrge Dómine ádiuva nos is sung after the Nunc dimíttis on Candlemas at the distribution of blessed candles, before the procession. But it doesn't appear in the 1962 Missal (nor Liber, despite the typological trouble of removing it).
It's not on the (few) list of “changes in the ’62” that I consulted, but I probably just missed it
It's even in the 1961 Liber (!), but not the 1962.
Gregory DiPippo admits (priv.comm.) that he doesn't know a formally stated reason, but guesses that it would be excised because it's not explicitly “about” the feast.
I also note that it's very nearly the introit for Sexagesima, always nearby and this year the following Sunday. But it's a different mode and really scarcely relevant.
It was part of the removal of the penitential elements from the procession (like the changing of the vestment colour from purple to white).
It is mentioned in one of the write-ups in Ephemerides Liturgicae (very useful publication for the 50s and 60s if you are looking at liturgical changes), but I would have to look up the exact reference.
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