DoorDash reported worse-than-expected fourth-quarter earnings on Wednesday.Jeffrey Greenberg/Universal Images Group via Getty ImagesDoorDash has a key advantage over Amazon in grocery delivery, CEO Tony Xu said Wednesday.The delivery service offers a wider variety owing to its myriad partnerships with grocers, Xu said.Amazon is ramping up its grocery delivery, creating more competition for DoorDash and Instacart.DoorDash …

