NEW YORK — The Astros’ tandem-starter experiment at Class AAA Oklahoma City has quietly ended. With former RedHawks starting pitchers Paul Clemens and Jose Cisnero on the Astros’ 25-man roster and OKC starter John Ely out for the year after Tommy John surgery, the Astros’ effort to use “piggyback” duos at Class AAA didn’t make it past late April. The Astros continue to use tandem starters at Class A and AA, though, and the organization never intended to use tandem starters at any level throughout the 2013 season. OKC starters Brett Oberholtzer and Dallas Keuchel briefly spent time with the Astros, while injuries to reliever Josh Fields and starter/long reliever [...]