oh, ok. i'm not in front of my setup right now so can't find it for you. however, it would almost certainly be inside the ftp directory, in the joomla directory, in a path SOMETHING like this:
components/community builder/templates/
then you would be looking (most likely) for php files. you'll have to sniff around until you find the one you're looking for. look for elements that you KNOW will be in there in plain text, for example, looking at a finished rendered list as a web page, almost all of it is dynamically rendered (meaning, it is being generated by querying the users database and will differ according to what information you asked it to pull), however, there is one static bit of text that i bet will be in the template in raw form: see where it says "1 user(s)" (or however many users you currently have registered)? the word "user(s)" is most likely hardcoded into the template.
so basically, sniff around all the template files and do searches for "user(s)" -- then once you find it, you'll know you're in the right location, and almost certainly, somewhere just under that, you'll find the code that generates the pulldown menu -- and you can remove it.
it'll take some detective work, but it's all in there somewhere!
make sure to work on a backup version of the file (or save the original) -- just in case you mess something up entirely. i often just duplicate the file and name one of them "originalfilename.phpOLD" - that way i know that if i ever mess up "originalfilename.php" i can just delete it, and go back to the OLD one.
good luck!