Spanish infrastructure giant Ferrovial announced it is offloading its remaining 25 percent stake in London's Heathrow Airport to a French private equity group and Saudi Arabia's sovereign wealth fund.Under the terms of the agreement, Ardian will buy 15 percent of FGP Topco, the holding company that controls the UK's busiest airport, and the Saudi public fund will take 10 percent, according to a statement released by the Spanish construction giant.