message: Remove some minor, unused code.
  I think this was left behind as part of
diff: @@ -46,8 +46,6 @@ pub struct Config {
  home_path: Filesystem,
  /// Information about how to write messages to the shell
  shell: RefCell<Shell>,
  - /// Information on how to invoke the compiler (rustc)
  - rustc: LazyCell<Rustc>,
  /// A collection of configuration options
  values: LazyCell<HashMap<String, ConfigValue>>,
  /// The current working directory of cargo
  @@ -113,7 +111,6 @@ impl Config {
  Config {
  home_path: Filesystem::new(homedir),
  shell: RefCell::new(shell),
  - rustc: LazyCell::new(),
  cwd,
  values: LazyCell::new(),
  cargo_exe: LazyCell::new(),
  