Molly’s Trolleys, a familiar sight on Pittsburgh streets for 22 years, is closing, effective Dec. 31. The Pittsburgh operation of the company, an outgrowth of a business school project by founder Molly Stahlman, was sold to the owners of Just Ducky Tours in 2011. Michael Cohen, Just Ducky co-founder, said in a prepared statement that both businesses “have been robust” but the success “has outpaced our ability to give both businesses the attention they need” and a strategic decision was…