Don't deny(warnings)

We already use `-- -D warnings` with clippy in CI, that's enough
breakage through new lints being introduced.

src/lib.rs

@@ -272,12 +272,11 @@
     html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
     html_favicon_url = "https://www.rust-lang.org/static/images/favicon.ico"
 )]
-#![cfg_attr(test, deny(warnings))]
 // When compiled for the rustc compiler itself we want to make sure that this is
 // an unstable crate
 #![cfg_attr(rustbuild, feature(staged_api, rustc_private))]
 #![cfg_attr(rustbuild, unstable(feature = "rustc_private", issue = "27812"))]
-#![deny(missing_debug_implementations, missing_docs, warnings)]
+#![deny(missing_debug_implementations, missing_docs)]
 
 use std::{borrow::Cow, cell::RefCell, env, io};