custom-login-page.php

<?php 

//Here's my custom CSS that removes the back link in a function
function my_login_page_remove_back_to_link() { ?>
    <style type="text/css">
        body.login div#login p#backtoblog {
          display: none;
        }
    </style>
<?php }

//This loads the function above on the login page
add_action( 'login_enqueue_scripts', 'my_login_page_remove_back_to_link' );