I’m afraid no override is possible for this file. You could use a custom script to remove all tabindexes though – although I am not exactly sure if that resolves it:
add_action('wp_footer', 'wp_footer_asp_custom_remove_tabindex', 9999);
function wp_footer_asp_custom_remove_tabindex() {
?>
<script>
(function($){
$('*[tabindex]').removeAttr('tabindex');
setTimeout(function(){
$('*[tabindex]').removeAttr('tabindex');
}, 1000);
})(jQuery);
</script>
<?php
}