Navigate to Calendar in Outlook 2013.
Select View tab on the top
Under the View tab, select Change View and click List.
A list of all entires in your Calendar displays. Select Categories which groups all your ‘holidays’ in the one section. Don’t want to delete any necessary business meetings!
Right click the Categories – Holidays heading and select Delete from the drop down list.
Note: You are not prompted to confirm this action… so ensure that you REALLY want to delete the holidays component in Categories.