Wendy's Co. and one of its biggest and oldest franchisees may be headed for a split. The Dublin, Ohio-based restaurant chain is suing Crofton-based DavCo Acquisition Holdings LLC and DavCo Restaurants LLC, saying the franchisee refuses to remodel its restaurants and invest in a company-wide point-of-sale system. "DavCo, a long-time franchisee of Wendy's, apparently believes that the guidelines announced by Wendy's, to be followed by all U.S. and Canadian franchisees, simply do not apply to it,"…