[DEPRECATING CHANGE] core: Remove unused Date.now fallback
[DEPRECATING CHANGE] core: Remove unused Date.now fallback

Bug: T184835
Change-Id: I1aa7047499c1e87c6957ca1502124e59f668121a

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