I just found this because I needed to also not allow customers the ability to register to the site. I looked at the tpl.create_account.php. Unfortunately that was not the correct file, at least partially not correct.
the file you want to edit, is tpl_login_default.php, this is the first file that gets used. This file calls the tpl_create_account.php file to display the create account form on the login page.
Also, there is a setting in admin > configuration > layout settings called "Use split-login page" which controls if the registration page shows on the page or shows a link to the create account page.
if you edit the tpl_login_default.php, there is a big if statement that determines how to show the page based on the above setting. I am keeping my setting to false and removing the code in the lower half of the page, from below <br class="clearboth" /> to just before the <!--EOF normal login --> comment. Leave the ending } in the php tags and the fina </div> otherwise you'll break the code and the layout.




