Move deny(warnings) into rustbuild

Mark-Simulacrum · Mark-Simulacrum · commit 1e466692c381 · 2018-04-08T16:59:14.000-06:00
This permits easier iteration without having to worry about warnings
being denied.

Fixes #49517
diff --git a/lib.rs b/lib.rs
@@ -46,7 +46,6 @@
        html_playground_url = "https://play.rust-lang.org/",
        test(attr(deny(warnings))))]
 #![deny(missing_docs)]
-#![deny(warnings)]
 
 #![cfg_attr(windows, feature(libc))]
 // Handle rustfmt skips
