A slowdown in U.S. drilling activity is taking a toll on the oil patch as Weatherford International PLC has become one of the biggest oil-and-gas bankruptcies in years. Among the world’s largest oil-field service companies, Swiss-based Weatherford filed for bankruptcy protection on Monday after bondholders approved a restructuring agreement that will reduce its total debt by almost $6 billion, or 70%. Five years ago, the company was worth more than $12 billion, but equity shareholders would be left virtually empty-handed if…