‘Billy Lynn’s Long Halftime Walk,’ adapted from the novel by Ben Fountain, isn’t so much a satire as an earnest indictment of a complicit culture.The movie exposes how, as spectators without risk or fear, in the guise of honoring our soldiers we appropriate for our own pleasure the thrill of bloodshed they’ve tasted.The film follows a day in the life of Army Spc. Billy Lynn who, along with the other members of Bravo Company, will be redeployed to Iraq as soon as they complete a “victory …