Don't deny warnings.

Author: reitermarkus

build.rs

@@ -1,5 +1,3 @@
-#![deny(warnings)]
-
 use std::{
     env,
     error::Error,

tests/tsan.rs

@@ -1,6 +1,5 @@
 #![deny(rust_2018_compatibility)]
 #![deny(rust_2018_idioms)]
-#![deny(warnings)]
 
 use std::{ptr::addr_of_mut, thread};