chore(tokio): warn on dead code

there is a module-wide allowance for dead code that seems to be a
holdover from when this was initially being written.

removing this does not unearth any warnings, and ideally any future
additions can be explicitly, and more narrowly, annotated accordingly if
need be.

Signed-off-by: katelyn martin <me+cratelyn@katelyn.world>

Author: cratelyn

src/rt/tokio.rs

@@ -1,4 +1,3 @@
-#![allow(dead_code)]
 //! Tokio IO integration for hyper
 use std::{
     future::Future,