Asia’s richest man Mukesh Ambani is overhauling a retail empire that sells everything from $0.20 soda to $5,900 Versace dresses, as he seeks to reassure investors antsy for an exit option in the form of a public listing.Slowing sales is a concern for Reliance Retail Ventures Ltd. after brokerages pegged its valuation as low as $50 billion — half the amount at which it last raised money two years ago....