Code to force non admin users to redirect from wp-admin

Admin Redirect.php

<?php
/*
Plugin Name: Admin Redirect
Description: Code to force non admin users to redirect out of wp-admin
Author: WPMU DEV
*/

add_action( 'wp', 'force_404' );

function force_404() {

if ( $_SERVER["HTTP_HOST"] . $_SERVER["REQUEST_URI"] == 'http://example.com/wp-login.php'
        || $_SERVER["HTTP_HOST"] . $_SERVER["REQUEST_URI"] == 'http://example.com/wp-register.php' 
            || $_SERVER["HTTP_HOST"] . $_SERVER["REQUEST_URI"] == 'http://example.com/wp-admin.php' ) 
            // The redirect codebase
            status_header( 404 );
            nocache_headers();
            include( get_query_template( '404' ) );
            die();

}