Perform the following steps:
Right-click on any Calendar Server
folder, then choose Manage Subscriptions from the
popup menu to open the Remote Calendar Subscriptions
window.
Select the calendar from which you want to unsubscribe.
Click on the Unsubscribe button.
Click OK to save your changes and close the Remote Calendar Subscriptions dialog.
Email and Calendar
deletes the selected calendar
from the specified Calendar Server
folder.