Merge branch 'fj-remove-wiki-page-created-at' into 'master'

Remove created_at from WikiPage

See merge request gitlab-org/gitlab-ce!22905

app/models/wiki_page.rb

@@ -151,12 +151,6 @@ class WikiPage
     last_version&.sha
   end
 
-  # Returns the Date that this latest version was
-  # created on.
-  def created_at
-    @page.version.date
-  end
-
   # Returns boolean True or False if this instance
   # is an old version of the page.
   def historical?