the allowed html tag list (with the corresponding css class) comes directly from the comment_form() code.
if you can find where the comment_form() is called (probably comments.php), you can change it there to remove the ‘comment_notes_after’.

there is no need for the theme to have this class anywhere in the css files.
if you want to use it, add it to the usual css file – in arras this is user.css.

Brother just input
.form-allowed-tags{
display:none;
}
your style.css file any position you can do it.