its first residency in Sin City on Friday night, the Irish icons dropped the new single “Atomic City” — and its video — earlier in the same day.Hey, they didn’t become one of the biggest rock bands of all time without learning a thing or two about promotional synergy.And as they prepare to go Vegas — where no respectable band would have dared to go back in the day when they ruled rock — “Atomic City” finds the quintessentially earnest quartet coming out swinging and swaggering rather than taking themselves so seriously.“I’m ready for bright lights…I came here for the fight/I’m front row in Las Vegas/And there’s a big one on tonight,” sings Bono in a not-so-subtle nod to “U2: UV Achtung Baby Live At Sphere,” their Sept. 29- Dec.