A little-known principal-investing team at Citigroup is being wound down, and the executive who led the group has left the firm, according to people familiar with the matter. What remains of Citi Credit Opportunities, a vestige of pre-financial-crisis banking that had $1 billion in its balance sheet to make loans to small and midsize companies, is being absorbed into the bank's broader financing operation. John Peruzzi, a nearly two-decade Citi veteran who led the team, has left the firm.