This summer’s annual Maine Lobster Festival parade will have its usual share of fire trucks, floats and marching bands — but you won’t see any politicians or political parties making their way down Main Street in Rockland. It’s the first time in the event’s 70-year history that organizers have imposed such a restriction, citing concerns raised by other parade entrants. Every August, the summer traffic in Rockland is rerouted away from the downtown to make way for the parade, which last year included Democrat Mark Eves, who showed up to press the flesh at the Maine Lobster Festival parade after announcing his candidacy for governor. Neither Eves nor any of his rivals in the gubernatorial race — or any other race — will be invited to take part this year.