Use language overrides shown below and override that language string to an empty value.
www.joomlapolis.com/blog/kyle/18701-language-overrides-have-arrived
Below are the language keys you'll want to override to get rid of the site count.
SITENAME_HAS_TOTAL_REGISTERED_MEMBERS
USERS_COUNT_MEMBERS
When userlists are rewritten in CB 3.x this will either just be gone entirely or be a parameter, but for now you need to use a language override.