Don't export View2D.getView2D

Small tidy-up. See https://groups.google.com/forum/#!topic/ol3-dev/wdyZgN2GuY4

Not sure whether the function is needed at all, but it is currently used in several places in the lib, so it can keep for the moment.
I'm surprised that the compiler doesn't complain here. getView returns an ol.IView, which doesn't have a setRotation method.