Open the Calendar app, then select the three lines top left. Within the list of calendars and the accounts you have stored, you should be able to view which account the holiday calendar is under. After finding the account, you can simply uncheck the category to remove the holidays. 
No worries! To add or remove categories to the Samsung calendar so that they don't appear in this list, it would depend on the account synced to that calendar. For instance, to change my calendar list I would go to https://calendar.google.com/calendar in desktop view.
