PROVIDENCE, R.I. — The Pawtucket Red Sox officially ended their pursuit for a proposed baseball stadium, club officials said on Saturday, terminating a monthslong campaign to build on a piece of public waterfront land in downtown Providence.The news of the dead deal came a day after House speaker Nicholas Mattiello said that negotiations between Rhode Island and the Triple-A affiliate of the Boston Red Sox had stopped weeks ago.In an emailed news release, PawSox officials said that Rhode Island Gov.