you shouldn't have done that....

This is just an informative message generated by MySQL and meant to tell developers that their DB structure could be more optimized, nothing really serious.

If disabling the debug_mode doesn't make the message disappear, you can remove it by setting the PHP config value mysql.trace_mode to Off.
If you don't have access to php.ini do it by adding the folliwing line to .htaccess in the root of your site: