Joomla has a default generic icon feature. You can hide it by blending it with the background colour. But doing so will make the article look unpleasant. So if you want to completely delete Joomla article generic item, then you can do it by editing the style sheet of the template.
Follow these steps to delete Joomla article generic item easily:
table.contentpaneopen td.contentheading { padding-left: 34px; }
background: url(../images/contentheading_ico.png) left top no-repeat;