Sorry, I thought it was still there, it will be removed in 3.4.7 - for now, edit css.php and find the following code (should be lines 3085-3093 in version 3.4.6)
HTML Code:
<?php if ( $bfa_ata['pngfix_selectors'] != '' ) { ?>
/* ------------------------------------------------------------------
---------- IE6 PNG FIX ----------------------------------------------
------------------------------------------------------------------ */
* html <?php echo $bfa_ata['pngfix_selectors']; ?> {
behavior: url("<?php echo $bfa_ata['template_directory']; ?>/js/iepngfix.php")
}
<?php } ?>
remove them and save the file