code: function(marker) {
          OpenLayers.Util.removeItem(this.markers, marker);
          if ((marker.div != null) &&
              (marker.div.parentNode == this.div) ) {
              this.div.removeChild(marker.div);    
          }
      }
docs: APIMethod: removeMarker
  
  Parameters:
  marker - {<OpenLayers.Marker.Box>}