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 think we should only include typecasts in our examples where they are strictly needed (i.e. where we get compilation errors otherwise).