MDL-80585 report_log: sanitize descriptions

Strip any HTML tags from values in the "Description" column.

report/log/classes/table_log.php

@@ -298,7 +298,7 @@ class report_log_table_log extends table_sql {
      */
     public function col_description($event) {
         // Description.
-        return $event->get_description();
+        return format_text($event->get_description(), FORMAT_PLAIN);
     }
 
     /**