In a major and potentially fatal setback to Gov. Jerry Brown’s $17 billion plan to build two huge tunnels under the Sacramento-San Joaquin River Delta, America’s largest irrigation district voted Tuesday to pull out of the project. The board of Westlands Water District, based in Fresno, voted 7-1 following an hour of debate and discussion over the costs of the project, which is intended to make it easier to move water from north to south.