v0.1.x: Don't deny warnings (#1368)

This is just too aggressive for a stable maintenance branch of tokio,
in that new rust release warnings are prooving too hard to fix.

tokio-threadpool/benches/basic.rs

@@ -1,5 +1,4 @@
 #![feature(test)]
-#![deny(warnings)]
 
 extern crate futures;
 extern crate futures_cpupool;

tokio-threadpool/benches/blocking.rs

@@ -1,5 +1,4 @@
 #![feature(test)]
-#![deny(warnings)]
 
 extern crate futures;
 extern crate rand;

tokio-threadpool/benches/depth.rs

@@ -1,5 +1,4 @@
 #![feature(test)]
-#![deny(warnings)]
 
 extern crate futures;
 extern crate futures_cpupool;

tokio-threadpool/src/lib.rs

@@ -1,5 +1,5 @@
 #![doc(html_root_url = "https://docs.rs/tokio-threadpool/0.1.16")]
-#![deny(warnings, missing_docs, missing_debug_implementations)]
+#![deny(missing_docs, missing_debug_implementations)]
 
 //! A work-stealing based thread pool for executing futures.
 //!