What’s Fleetwood Mac without some world-class drama? Until a few years ago, the missing piece of a reunited Fleetwood Mac puzzle was Christine McVie, who’d stopped touring because of a fear of flying. Now that the “Songbird” is back, however, guitarist/vocalist Lindsey Buckingham was “involuntarily expelled” from the band in January, and is suing. The classic-rock legends, who crafted some of the most beloved guitar-pop hits of the baby-boomer generation, continue to tour without Buckingham — and they’ve enlisted some high-quality hired hands. Neil Finn of Crowded House is filling in on vocals, and undersung guitar hero Mike Campbell, of Tom Petty’s Heartbreakers, is adding new fire to the time-tested licks