By default createURLAnnotation will create a cell with a solid border around it. This is controlled by the haruAnnotation object returned by the method. Create a reference to the haruAnnotation object and alter the border style to remove the solid border.
<?php
$haruAnotation = $currentHaruPage->createURLAnnotation(Array($leftX,$bottomY,$rightX,$topY),'http://'.$dataItem);
$haruAnotation->setBorderStyle(0, 0, 0); // this alters the border
?>