Bug1035492-[Wallpaper]-Use Img element instead of background images for gecko to handle decoded image memory r=djf

This concerns me. If we're reducing the image size to 33% in width, we shouldn't be setting the height to an absolute value or we might distort the images. Different devices will have different aspect ratios. So the fact that this line is here (regardless of its value) indicates that we are distorting the wallpaper on at least some devices. 

If we just use an img element in place of this div, then I suspect that just setting the width will do the right thing for the height and we don't have to set it at all.