WikimediaUI theme: Make checkbox/radio code leaner
WikimediaUI theme: Make checkbox/radio code leaner

Making Checkbox- and RadioInputWidget's code leaner by
reordering pseudo-classes and therefore removing
unnecessary specificity overrides.

Change-Id: Ia60a7953a4c1dad64616f974f24cc901aa2921e9

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui