The default behavior in a WordPress blog is to inform users who may like to leave a comment, that some HTML tags are allowed. If you do not want this information displayed you have to change the WordPress system code, which means that in the next system update you will lose your changes. To remove these directions for HTML tags in comment forms you can also add a simple direction to your theme’s style.

.form-allowed-tags{display:none;}

Yet again you will lose your code, when you change theme or your current theme is updated. The best way would be to use a plugin that enters custom code to the top (head) area of each and every page automatically. Here is the code you should use in this case:

 <style type='text/css'>
.form-allowed-tags{display:none;}
</style>