PopupWidget: Remove references to 'show' and 'hide' events
PopupWidget: Remove references to 'show' and 'hide' events

These were killed back in the dialog refactor in July (Id121fc3a), but the documentation remained.

Bug: 72168
Change-Id: I91c890110e0c049e9150d5be4c61404aacef2906

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