Disable comments

function.php

// Disable support for comments and trackbacks in post types
function lf_disable_comments_post_types_support() {
	$post_types = get_post_types();
	foreach ($post_types as $post_type) {
		if(post_type_supports($post_type, 'comments')) {
			remove_post_type_support($post_type, 'comments');
			remove_post_type_support($post_type, 'trackbacks');
		}
	}
}
add_action('admin_init', 'lf_disable_comments_post_types_support');

// Close comments on the front-end
function lf_disable_comments_status() {
	return false;
}
add_filter('comments_open', 'lf_disable_comments_status', 20, 2);
add_filter('pings_open', 'lf_disable_comments_status', 20, 2);

// Hide existing comments
function lf_disable_comments_hide_existing_comments($comments) {
	$comments = array();
	return $comments;
}
add_filter('comments_array', 'lf_disable_comments_hide_existing_comments', 10, 2);