You can't just remove that activity type all over the CRM system.
But at least you can override the "Add Activity" button to only show the activity types that you prefer.
http://crmpiecemeal.wordpress.com/2012/07/18/removing-unwanted-activity-types-from-crm-2011-online/
https://community.dynamics.com/crm/f/117/t/64490.aspx