Stop using <activity:subject> for atom feeds

lib/atom10feed.php

@@ -146,15 +146,16 @@ class Atom10Feed extends XMLStringer
     }
 
     /**
-     * Add a activity feed subject via raw XML string
+     * Deprecated <activity:subject>; ignored
      *
      * @param string $xmlSubject An XML string representation of the subject
      *
      * @return void
      */
+
     function setActivitySubject($xmlSubject)
     {
-        $this->subject = $xmlSubject;
+        throw new ServerException(_('Don\'t use this method!'));
     }
 
     function getNamespaces()

lib/atomgroupnoticefeed.php

@@ -85,8 +85,9 @@ class AtomGroupNoticeFeed extends AtomNoticeFeed
         $this->setId($self);
         $this->setSelfLink($self);
 
-        $this->addAuthorRaw($group->asAtomAuthor());
-        $this->setActivitySubject($group->asActivitySubject());
+        $ao = ActivityObject::fromGroup($group);
+
+        $this->addAuthorRaw($ao->asString('author'));
 
         $this->addLink($group->homeUrl());
     }

lib/atomusernoticefeed.php

@@ -60,8 +60,8 @@ class AtomUserNoticeFeed extends AtomNoticeFeed
         $this->user = $user;
         if (!empty($user)) {
             $profile = $user->getProfile();
-            $this->addAuthor($profile->nickname, $user->uri);
-            $this->setActivitySubject($profile->asActivityNoun('subject'));
+            $ao = ActivityObject::fromProfile($profile);
+            $this->addAuthorRaw($ao->asString('author'));
         }
 
         // TRANS: Title in atom user notice feed. %s is a user name.