In a surprise to basically no one, Tom Cruise rides a motorbike off a cliff in the summer blockbuster “Mission: Impossible — Dead Reckoning Part One,” which was released in theaters this summer after three years of stop-and-start production and is now beginning its life on home video. The action superstar insists on doing his own stunt work, and has been talking about it since 1996, the year the first “Mission: Impossible” movie came out. In each successive movie, the stunts have gotten more intense: hanging off the tallest building in the world, attaching himself to the outside of an airplane while it takes off and flying his own helicopter through a treacherous mountain range.