Elaine Low Senior TV WriterSPOILER WARNING: Do not read if you have not seen Season 1, Episode 4 of “The Falcon and the Winter Soldier,” streaming now on Disney Plus.Arguably one of the grittiest moments in the MCU films — or what counts for gritty in this world, anyway — comes in the form of Steve Rogers, Bucky Barnes and Tony Stark duking it out at the end of “Captain America: Civil War.”After Helmut Zemo (Daniel Brühl) reveals that a brainwashed Bucky Barnes (Sebastian Stan) had years ago