Forget the death of the PC: BlackBerry chief executive Thorsten Heins thinks tablets are on their way out as users shift to doing more through their smartphones, the Washington Post reports. In comments at a Milken Institute conference, Heins said smartphones will become users’ main source of computing power in the next five years. People will simply plug whatever display, keyboard or other accessory they need to do their work into a smartphone. For many workers, a smartphone will be the only device they need, he said…