NEW YORK — Landmark Theaters president and CEO Paul Richardson and exec VP Burt Manzari said Thursday they’re leaving the arthouse movie chain as of May 25.Landmark was acquired by entertainment investors Todd Wagner and Mark Cuban last September from Oaktree Capital for $80 million. At the time, contrary to an initial report, it appeared that Richardson and his team were set to stay on for the foreseeable future. “Burt and I wish Todd the best,” Richardson said. Wagner wasn’t immediately available for comment. Along with the 185-screen Landmark, Wagner and Cuban operate 2929 Productions and hold a sizable stake in Magnolia Pictures, an indie film distrib that owns three arthouses.