LOS ANGELES — “Captain America: Brave New World” kept falling but still hovered above all others at a weak weekend box office. The latest Disney-Marvel offering brought in another $15 million according to studio estimates Sunday, when most of Hollywood’s attention was on the Oscars. The Anthony Mackie-led “Captain America: Brave New World” opened strong at about $120 million on a three-day weekend last month, but plunged to $28.2 million last week in one of the most significant second-week drops for a Marvel movie. It’s earned $163.7 since its release. It was slammed by many critics and audiences, failing to