One of the Extra Theme’s features is the ability to use the Divi Builder to layout category pages. However, you’ll find if you try to edit the layout that there is no way to remove the “CATEGORY: NAME” heading. Fortunately, this can easily be removed by adding the following CSS to Extra (e.g. in Extra > Theme Options > General Settings > Custom CSS):

body.category .et_pb_extra_column_main > h1:first-child { 
    display: none;