You have three ways to go:
1) Leave as is.... keeping anti freeze in the water heater will do no harm.
2) Remove the anode rod and let the antifreeze drain out. You will notice that the anode rod is about an inch above the bottom of the water heater so there will be antifreeze in the WH over the winter anyway. If you want you can remove the last inch of liquid by inserting a cotton string or twisted paper towel PARTIALLY into the drain hole and having the lower end of the string below the level of the tank. This will allow all the anti freeze to drip out using a siphon action. This may take over night.
3) Do as in #2, but use a funnel and bucket to catch the antifreeze that drains from the water heater. This can be saved and used next year........ just in case you never learn the correct way to by pass the water heater. You will have at least 6 gallons of anti freeze to save.
My trailer takes 2 gallons to winterize with the bypass closed. It takes 12 gallons with the bypass open (I have a 10 gal WH).