If you want to delete the public holidays from holiday calendar,
1. Go to the 'Setting'.
2. Click 'Policies' and choose the policy you want to change.
3. Under 'Leave' section, click on 'edit' icon of holiday calendar.
4. Delete the holidays and click 'import '.
5. Finally, Click 'Update Policy' and 'Confirm'.
Please refer following tutorial video in details: