Dashicons is the official icon font of the WordPress.

There are two ways.

1. Custom code in function.php

add_action('wp_enqueue_scripts', 'ec_disable_dashicons');

function ec_disable_dashicons(){

    if(!is_user_logged_in()) {

        wp_dequeue_style('dashicons');
    wp_deregister_style('dashicons');
    }
}

2. Using EC Addons