message: Remove another `FnBox` trait
  No longer needed on stable!
diff: @@ -12,17 +12,7 @@ pub struct Job {
  /// Each proc should send its description before starting.
  /// It should send either once or close immediately.
  pub struct Work {
  - inner: Box<dyn for<'a, 'b> FnBox<&'a JobState<'b>, CargoResult<()>> + Send>,
  -}
  -
  -trait FnBox<A, R> {
  - fn call_box(self: Box<Self>, a: A) -> R;
  -}
  -
  -impl<A, R, F: FnOnce(A) -> R> FnBox<A, R> for F {
  - fn call_box(self: Box<F>, a: A) -> R {
  - (*self)(a)
  - }
  + inner: Box<dyn FnOnce(&JobState<'_>) -> CargoResult<()> + Send>,
  }
  impl Work {
  @@ -38,7 +28,7 @@ impl Work {
  }
  pub fn call(self, tx: &JobState<'_>) -> CargoResult<()> {
  - self.inner.call_box(tx)
  + (self.inner)(tx)
  }
  pub fn then(self, next: Work) -> Work {
  