Remove lint annotations in specific crates that are already enforced by rustbuild

Remove some random unnecessary lint `allow`s

src/libtest/lib.rs

@@ -17,7 +17,6 @@
 // this crate, which relies on this attribute (rather than the value of `--crate-name` passed by
 // cargo) to detect this crate.
 
-#![deny(rust_2018_idioms)]
 #![crate_name = "test"]
 #![unstable(feature = "test", issue = "27812")]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/", test(attr(deny(warnings))))]