By Deepa Seetharaman and Alexei Oreskovic SAN FRANCISCO (Reuters) – David Marcus, who has led eBay Incs fast-growing payments unit PayPal for the past two years, will step down this month to run Facebook Incs messaging products, the companies announced on Monday. Under Marcus, PayPal has moved more aggressively into the physical world by developing a mobile wallet for consumers as well as point-of-sale systems for retailers. The move marks Facebooks latest effort to bolster its private messaging features as it faces competition from a new crop of popular mobile messaging services such as Snapchat and Line.