J. Ezra Merkin may have yet to bear his soul over any guilt he feels for placing more than $2 billion of investors’ money with Bernie Madoff, but he’s being forced to bare his walls. Merkin, who is among the world’s leading collectors of Mark Rothko paintings, is selling the core of his art collection in a private sale expected to fetch roughly $310 million-money that will go toward paying off liens on the art and to help pay back some of investors’ losses.