There aren't any options to do that, but you can perform this little hack-

The tabs displayed when viewing a project are created in a file called application\helpers\project_website.php

Find these lines, and remove them:

add_tabbed_navigation_item(new TabbedNavigationItem(
  PROJECT_TAB_TAGS,
  lang('tags'),
  get_url('project', 'tags')
));

That will remove the tags tab. It will not remove tag support, so you'll still have the option to add tags to a message and such. To completely remove tags would take a lot more work. Also, when you upgrade, your tags tab will come back.