Disabled default cubemap [Obsolete]

This addon is no longer needed. The overly shiny DEFAULT cubemaps no longer appear in the game. You might come across cubemaps on some maps that appear super bright, but this is a separate issue and this addon would have never fixed them. Only the default cubemap textures (the ones that look like sunset in a desert) would have gotten fixed. No more extremely shiny objects on maps with default cubemaps! Maps with actual built cubemaps won't be affected. Mat_specular 0 disables all cubemaps. This addon only replaces the default cubemap with a pitch-black one.