Keith,
This can be done in multiple ways. You can use Custom CSS that removes the button or even easier, you can utilize the New Profiles functionality that will allow you to remove buttons from the toolbar ribbon and similar. Here is a some information on Profiles...
User Manual link: http://usermanual.clarizen.com/profiles-overview
Video Tutorial: https://success.clarizen.com/entries/88326538-Clarizen-Profiles-Tutorial