HSBC is winding down its business banking unit in the U.S. to focus on other markets.The bank laid off 40 employees and informed 4,400 clients of the unit's closure.HSBC has been exiting some international markets to concentrate on Hong Kong, the U.K., and Asia.Earlier this year, HSBC stopped advising companies on deals in the U.S. and Europe, sold its U.S. retail banking business, and Canadian operations.