Vacation and Sick Leave entries are tracked on a calendar year basis, not fiscal year, and are automatically dropped from the YTD reports for the current year when the year changes, however, if you want to actually delete all the vacation/sick leave records, you can certainly do that, though doing so will mean if you run the Previous Payroll reports for date ranges within those time frames, those reports would no longer include those vacation/sick leave records.
If you want to delete all the vacation/sick leave records, go to the Time Clock Entries screen, click the "Find" button at the bottom of the screen, enter "Approved" in Status field, hit the return key. Review to ensure the "found records" are the ones you want to delete. You can delete them one at a time or if you're sure you want to delete ALL the records that you've found at one time, you can hold down the "Ctrl" key while clicking the "Delete" button and all the found records will be deleted. That action can't be undone, so make sure you're deleting the records you really want to delete.