Remove commment support from post, pages, admin menu and admin bar.

remove-wp-comments.php

<?php

/* Remove Comments Tab from admin menu */
function rtp_remove_admin_menus() {
    remove_menu_page('edit-comments.php');
}
add_action('admin_menu', 'rtp_remove_admin_menus');


/* Remove commment support from post and pages */
function rtp_remove_comment_support() {
    remove_post_type_support('post', 'comments');
    remove_post_type_support('page', 'comments');
}
add_action('init', 'rtp_remove_comment_support', 100);


/* Remove comment link from admin bar */
function rtp_admin_bar_render() {
    global $wp_admin_bar;
    $wp_admin_bar->remove_menu('comments');
}
add_action('wp_before_admin_bar_render', 'rtp_admin_bar_render');