:Gavia immer is not an administrator, but undid an administrative closure, without even bothering to notify me. So, protection is appropriate. 
 :As to the discussion itself. What you actually want to do is to change the first letter in the word "history" to "H". For such discussions there exists a special board. That this change can be accomplished by deleting the page instead of simply editing it is only a technicality. The deletion will replace it with a default message. So, I can say that it is not possible, in fact, to delete a MediaWiki message—it is only possible to replace it with the default. 
 :I am also worried about the level of participations. Can really 3 editors decide what many thousands of others will see? Such a discussion needs a wider forum, where more people can participate. I suspect that only few editors knew that this discussion was taking place on an obscure MfD page. MediaWiki namespace contains such page as MediaWiki:Common.js, which I do not think should deleted via MfD. 
 :The instructions on MfD page concern only MediaWiki pages that are not system pages. (It is possible to create a MW page with an arbitrary name.) The past examples you mentioned above were mainly about such pages. _