message: Improve RustDocFingerprint::remove_doc_dirs
  We were not filtering the cases where the doc folder
  paths did not exist.
  Also, we were overrwriting the error when it doesn't
  make sense. We now return the first one by folding the
  results of the doc_dirs removal resolutions.
diff: @@ -774,16 +774,13 @@ impl RustDocFingerprint {
  }
  fn remove_doc_dirs(doc_dirs: &Vec<&Path>) -> CargoResult<()> {
  - let errs: Vec<CargoResult<()>> = doc_dirs
  + doc_dirs
  .iter()
  + .filter(|path| path.exists())
  .map(|path| paths::remove_dir_all(&path))
  .filter(|res| res.is_err())
  - .collect();
  - if !errs.is_empty() {
  - Err(anyhow::anyhow!("Dir removal error"))
  - } else {
  - Ok(())
  - }
  + .collect::<CargoResult<Vec<()>>>()
  + .map(|_| ())
  }
  /// This function checks whether the latest version of `Rustc` used to compile this
  