Remove an unused arg from visit_fn()
Remove an unused arg from visit_fn()

aidancully/rust,rust-lang/rustfmt,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,SingingTree/rustfmt,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,SingingTree/rustfmt,graydon/rust,rust-lang/rustfmt