To take the wings off of your pegasus, you have to go to the bottom right of your pegasus' page. You should see a box like the one pictured on the right. Click remove, and your pegasus will become a regular horse, and you will now have a new ingredient.
Warning: If you remove the wings from the pegasus, you will never be able to get them back without buying another Medusa's Blood . Removing wings from a Golden Apple pegasus results in the loss of the GA coat plus the bonuses from the GA. You will only be able to get the GA back by purchasing another one.
The only other way to obtain the Pegasus' wings ingredient is to pay a large price for them at the flash sales. However, there were only a few for sale, making the wing-removing option easier and cheaper. The event lasted from 27th May 2013 to 13th June 2013.