Fix for #6879228 added several methods that had implied to be used in the future RFE's.
However after careful investigation it became clear that those methods are unnecessary
and only overburden the API.

Methods to be removed in the LayerUI class:

repaintLayer(),
paintLayer(Graphics2D g2, JLayer<? extends V> l),
configureGraphics(Graphics2D g2, JLayer<? extends V> l)