Remove strip_tags warning on Special:RecentChanges

Structure of the 'content' key returned from formatters changed
in d2f48911a254460c02e1d16cb6395e53c538bcd5.  Patch updates
RecentChanges formatter to use this.

Change-Id: Iab2952a5b17fe4dffd0868b0c61858dc9c3932d7
Merge "Remove strip_tags warning on Special:RecentChanges"