message: remove suppression of clippy lint `too_many_arguments`
diff: #![warn(rust_2018_idioms)] // while we're getting used to 2018
  -#![allow(clippy::too_many_arguments)] // large project
  #![allow(clippy::redundant_closure)] // there's a false positive
  #![warn(clippy::needless_borrow)]
  #![warn(clippy::redundant_clone)]
  