Rename `ClippyArgsCallbacks` to `RustcCallbacks`
Rename `ClippyArgsCallbacks` to `RustcCallbacks`

aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust