Is a reboot afoot? Fans of the BBC’s “Sherlock,” which propelled Benedict Cumberbatch, as the titular detective, into the zeitgeist both in and out of the U.K., might still be seeking one last adventure for Holmes and Watson (Martin Freeman). But for Louise Brealey, who starred as pathologist Molly Hooper — whose loyalty to Sherlock was matched only by her unrequited love for him — getting the band back together again seems a tall order. “We lost Una Stubbs [who played Mrs. Hudson]. And so in some regards, it’s sort of unimaginable without her because of course it’s Sherlock and Watson, but al…