MDL-85416 assignment: fix date format in messages

For no very obvious reason, the date in the 'You have just
submitted your assignemnt' message was formatted differently
from the default used on-screen.

This commit makes it consistent.

mod/assign/locallib.php

@@ -6565,7 +6565,7 @@ class assign {
         }
         $info->assignment = format_string($assignmentname, true, array('context'=>$context));
         $info->url = $CFG->wwwroot.'/mod/assign/view.php?id='.$coursemodule->id;
-        $info->timeupdated = userdate($updatetime, get_string('strftimerecentfull'));
+        $info->timeupdated = userdate($updatetime);
 
         $postsubject = get_string($messagetype . 'small', 'assign', $info);
         $posttext = self::format_notification_message_text($messagetype,