Deleting Certain terms from appearing on the front end as links

The function get_terms has a convenient $args parameter which allows you to customize your query to meet your needs; in your case, it would be something as simple as:

$args = array(
    'exclude'       => array(1,2,3)
);

$terms = get_terms("testimonial_category", $args);

The array to exclude must contain the category ids of the categories you wish to leave out.