How to remove the depreceated target="_blank" in Wordpress TinyMCE?

/** Creating custom :external selector **/
$.expr[':'].external = function(obj){
 return !obj.href.match(/^mailto\:/) && (obj.hostname != location.hostname); };
// Add 'external' CSS class to all external links.
$('a:external').bind('click', function(){
 open(this.href);  return false;
});