Disable WordPress admin bar for all users except for administrators. Source: http://www.wpbeginner.com/wp-tutorials/how-to-disable-wordpress-admin-bar-for-all-users-except-administrators/

disable-admin-bar-except-admins.php

<?php

//* Disable WordPress admin bar for all users except for administrators
function customprefix_remove_admin_bar() {
    if (!current_user_can('administrator') && !is_admin()) {
        show_admin_bar(false);
    }
}
add_action('after_setup_theme', 'customprefix_remove_admin_bar');