SystemUI: remove statusbar gradient, fix SystemUI FC's on hdpi and below

as http://goo.gl/cWTqEQ only added xhdpi and xxhdpi, we end up with FC's at
lower dpi's such as hdpi, mdpi, ldpi

also the gradient is ugly :P

Change-Id: Ic45e2caa16ea27fff683e6e0ed444069c368c6cc