message: Simplify test error output
diff: @@ -143,8 +143,6 @@ fn failures_to_outcome(failures: &[TestFailure]) -> libtest_mimic::Outcome {
  } else {
  let mut msg = String::new();
  - writeln!(msg).unwrap();
  - writeln!(msg, "failures:").unwrap();
  writeln!(msg).unwrap();
  for failure in failures {
  writeln!(msg, " {}:", failure.name).unwrap();
  