WASHINGTON — When White House chief pastry chef Bill Yosses left the executive mansion last summer, the president publicly mourned the loss of “the crust master’s” mysteriously addictive pies. And when the first family’s personal chef and pal, Sam Kass, left in December, Michelle Obama heaped praise on Kass’ “extraordinary legacy of progress” in an official White House statement. But the recent exit of head florist Laura Dowling, who’d been in the job since 2009, has been a much quieter affair. So hush-hush, in fact, that most outside of 1600 Pennsylvania Ave. knew nothing about it. There’s still no official...