It is the height of irony that valerian, the flowering plant that lends its name to the hero of Luc Besson’s sci-fi extravaganza “Valerian and the City of a Thousand Planets,” is sold in health-food stores as a sleep aid. Anchored by a drowsy, half-lidded performance by Dane DeHaan, who renders the monotone title character as if he were a patient shuffling through his own private hospital with an I.V.