XWIKI-20030 : Notification events contain invalid alt attribute on user profile picture

* Use the plain user name as the alt attribute of the user profile
  picture
* Make sure that only one link to the user profile is added in each
  event

xwiki-platform-core/xwiki-platform-web/xwiki-platform-web-templates/src/main/resources/templates/notification/macros.vm

@@ -172,12 +172,8 @@
   #set ($userDoc = $xwiki.getDocument($user))
   #getUserAvatarURL($userDoc.documentReference, $avatarURL, 40)
   #set ($userName = $xwiki.getUserName($user))
-  #if ($userDoc)
-    #set ($displayedUser = "<a href=""$userDoc.getURL()"">$userName</a>")
-  #else
-    #set ($displayedUser = $userName)
-  #end
-  <span class="notification-event-user"><img src="$avatarURL.url" alt="$escapetool.xml($userName)"/>#if(!$onlyAvatar)${displayedUser}#end</span>##
+  #set ($plainUserName = $xwiki.getPlainUserName($user))
+  <span class="notification-event-user"><img src="$avatarURL.url" alt="$escapetool.xml($plainUserName)"/>#if(!$onlyAvatar)${userName}#end</span>##
 #end
 #**
  * Display a line with the name of all users