Revert "[SPARK-13760][SQL] Fix BigDecimal constructor for FloatType"

This reverts commit 926e9c45.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala

@@ -748,7 +748,7 @@ case class Round(child: Expression, scale: Expression)
         if (f.isNaN || f.isInfinite) {
           f
         } else {
-          BigDecimal.decimal(f).setScale(_scale, HALF_UP).toFloat
+          BigDecimal(f).setScale(_scale, HALF_UP).toFloat
         }
       case DoubleType =>
         val d = input1.asInstanceOf[Double]