Wynn Resorts is in the process of “rightsizing” operations at Encore Boston Harbor, the $2.6 billion casino that opened just six months ago but has so far fallen short of revenue projections, a company official said Thursday. Eric Kraus, the casino’s senior vice president of communications, told the state’s Gaming Commission that one change the casino is pursuing is using automated drink dispensers, a move that he said would speed up drink service for gamblers but also replace an undetermined number of “back of the house” bartenders and other staff.