Remove User Groups option from checkout page

Opencart 1.5.6.4
Theme Journal2

I have 2 User Groups in my shop. Default and Wholesale. I want to let people choose from default or wholesale when on the Register Account page, but not when they are on the Checkout page. On the checkout page I want that option completely removed, so they end up in the default User Group.

Is there a way to do this? I don't know what files to look in. I looked at my theme checkout.tpl but don't know where to start. A CSS display:none; would be great, if I knew where to put it.

Thanks!!

I have same problem. Hoping for some help. to remove user group in checkout page