Update basicOperators.scala

Author: YanjieGao

sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala

@@ -217,6 +217,4 @@ case class Subtract(left:SparkPlan,right:SparkPlan) extends SparkPlan {
   override def execute() = {
     left.execute().subtract(right.execute())
   }
-
-  override def otherCopyArgs = sc :: Nil
 }