How to Remove Site Name from Sign-up Step 2

I saw something about this on one of my searches in the forums but can't find it now.

When a new user signs up for a new blog, they enter their username/sitename on the first page, but them on page 2 it shows this in an editable field.

Is there a way to not display this field on the second part of signup so that usernames and site names are identical and the new user isn't tempted to make their site name different?

Thanks.

Martin