This style block appears to only contain the SelectedRowColor property value when changed in the IDE. If you want to change the selected row color, what’s wrong with doing that via the IDE’s inspector? Or is the goal to set a certain cell’s color?
If you do want to just remove it, add this to the Shown event of your WebListBox:
ExecuteJavaScript( "$('#" + me.ControlID + "_style').detach();" )