Chris,
My best suggestion would to be to go into the Joomla -> Language Manager -> Overrides and search for the string you want to alter. Then, set the string to blank. I think that should work. If not, you may need to alter the com_users code to prevent that string from showing.. which isn't as much fun or recommended if not necessary.
I hope that helps get you started, but if you need more assistance, just let us know.
Thanks,
Alex