Immediately delete cache keys if either of the relevant two Refreshed-specific interface messages gets deleted

Previous cache invalidation code invalidated cache when either [[MediaWiki:Refreshed-navigation]] or [[MediaWiki:Refreshed-wiki-dropdown]] was edited.
However, nothing was handling page deletion, so if the messages got deleted, cached data would still be displayed for up to 24 hours.

Change-Id: I5a7823b864afebd43500d0707ff77e25ff8a0a1e