After an 18-year tenure, Nike will be removed from the S&P 100 later this month. But during a panel at the Fast Company Innovation Festival in New York City this week, Phil McCartney, Nike’s chief innovation, design, and product officer, maintained that the company’s best days remain ahead. The secret sauce fueling this turnaround, he said, is a renewed focus on Nike’s engagement with athletes. What’s the rediscovered North Star for the company…