CHICAGO — The second day of Lollapalooza opened with questions swirling outside the Grant Park gates about the music festival’s future in Chicago, and about contract talks between Texas-based producer C3 Presents and the city. Inside, the focus was on the experience and the music. Headliners Friday were Machine Gun Kelly, Bob Moses, Rezz and Dua Lipa. Unlike in pre-pandemic summers, single-day general admission tickets are not yet sold out, and available through Sunday on the festival’s website. (Tickets can also be found for sale online, some at discounted prices.) Lollapalooza has played in …