SkyDrive Inc., a Japanese air taxi startup, on Thursday cited persistent challenges in addressing safety and other technological development issues as the reason for abandoning its plan to offer commercial flights at next year’s World Exposition in Osaka. SkyDrive sought to develop a flying taxi that can carry up to three people to showcase its technology at the expo as one of the event’s main attractions, but it decided last month to withdraw the plan and only perform demo flights without passengers. “As we moved ahead with the development, we found more and more unexpected problems, includin…