Tucked away among the tilled plots and scrubby pastures of this rural town, the Seattle Mariners’ baseball academy is mostly abandoned. The weight room has been cleared of machines. The numbered locker-room stalls are bare. One afternoon last week, a grounds crew pulled out bases from the main field while workers packed away a few stray trophies, bats and uniforms. But the teenage prospects who shared bunks here just three weeks ago are gone, shipped off to a newer school in the Dominican Republic.