Introduced in Charitable 1.8.1.16, you can now hide the area on the donation form that can appear reminding donors to register to save future donation settings (the same area also shows a login form).

Filter

You can add a filter like this (via WPCode or add to your functions.php file) to disable the form template from being loaded in the donation form.

add_filter( 'charitable_donation_form_login_allow', '__return_false' );

Setting

To do this without code there is a new setting (in beta as of 1.8.1.16) that you can toggle as well. This can be found in the “General” tab in Charitable settings.