No it is no longer needed, and this really annoyed me, because I spent lots of time and money getting mine organised and specially sent over, after ringing round embassy´s and getting the list of papers needed, which allllll stated I needed my BC, legalised, translated and then legalised again here. but when I went just the other week to complete my papers they never asked me for it, and instead asked me to make a full photo copy of my entire passport. which is, as others have stated a better piece of identification as it has all the same details as your BC and is international, so without the need of the translation and legalisation steps. But yeah when I asked him... what about my BC, he just said no we´re no longer using them any more.
So yeah certainly for the migracion office in BsAs, you no longer require your BC
