Permethrin will kill maggots on contact. Most feed stores have permethrin spray or the concentrate to mix with water. A horse product, SWAT which has pyrethrins, also works. I would remove any chicken with a wound to a place where there are no flies.
Most deep wounds are cleaned with Hibiclens and water, weak betadine, or saline, and keep moist withplain Neosporin or Triple Antibiotic Ointment twice a day. A clean towel or puppy pad is perfect for bedding in a dog crate when they wound is open. Deep wounds usually heal from the inside out as the tissue granulates in and comes together.