To fully appreciate just how successfully the ouster of the Occupy Boston encampment in Dewey Square unfolded over the past few days, it’s important to note not only what happened, but what didn’t. Boston officials, as well as Boston’s protesters, avoided so many of the problems that plagued cities across the nation as the Occupy encampments lurched toward their typically bitter ends. Some of it is, of course, luck. Much more of it owes to a combination of skill on the part of police officials and uncommon restraint on the part of the cops on the ground. Boston Police accomplished something even greater than reclaiming a visible swath of public parkland: It pushed its own checkered history of crowd control a little bit further into the realm of past tense.