Rather than report this information in the local section, I would move it to Box 14 of your W-2. Use WA L&I as the description, enter the amount, and for category select Other (not classified) from the pulldown menu. This is the amount you pay into the state workers' compensation fund. It will not have any impact on your taxes.
You can then click the trashcan next to the local information in Boxes 18-20 to get rid of it.
