unused import

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1897137 13f79535-47bb-0310-9956-ffa450edef68

poi/src/main/java/org/apache/poi/ss/util/cellwalk/CellWalk.java

 import static org.apache.commons.math3.util.ArithmeticUtils.mulAndCheck;
 import static org.apache.commons.math3.util.ArithmeticUtils.subAndCheck;
 
-import org.apache.commons.math3.util.ArithmeticUtils;
 import org.apache.poi.ss.usermodel.Cell;
 import org.apache.poi.ss.usermodel.CellType;
 import org.apache.poi.ss.usermodel.Row;