Never delete entries posted in a previously closed year. If the 2005 entries are not affecting the Vacation pay currently available to each employee, there is no need to remove or adjust it. They were likely created to adjust incorrect accrual and/or pay out, or used to create beginning balances for payroll if you started using QB payroll part way through a calendar year.
If the Vacation Accrued or Paid Out amount is incorrect, it can be adjusted in each employee's profile. Make sure the report you are viewing is set to ALL as opposed to a specific time period.