By Justin Barrasso The Weekly Takedown previews Holm’s bout vs. Ketlen Vieira and reveals exclusive news on the Polaris 20 main event. View the original article to see embedded media. Welcome to The Weekly Takedown, Sports Illustrated’s in-depth look at MMA. Every week, this column offers insight and information on the most noteworthy stories in the fight world. Holly Holm’s goal extends far beyond this Saturday’s bout against Ketlen Vieira. “I want to be the one who does what’s never been before,” Holm said. “I wanted to win world titles in boxing and MMA, and I was able to do that. Women in …