pnCCD preview: output 2D

I just noticed that for pnCCD preview, I get the multi-frame widget in Karabo GUI (complete with interesting take on what is the "Y" dimension):

Previews used to all have the frame selection feature, so _preview_data_views for PnccdCpuRunner adds np.newaxis to allow this (even though there's not much to select). But now that PnccdCorrection._preview_outputs has PreviewSpecs with frame_reduction=False, the view can just already be 2d as no frame slicing will be done anyway. Should be simple fix. Also check ePix.