Remove debug crate

This fixes errors with latest 0.13.0-nightly as crate has been removed:

`error: can't find crate for ‘debug’`

examples/concurrent-server.rs

@@ -1,7 +1,6 @@
 #![feature(macro_rules, default_type_params)]
 
 extern crate hyper;
-extern crate debug;
 
 use std::io::util::copy;
 use std::io::net::ip::Ipv4Addr;

examples/server.rs

@@ -1,7 +1,6 @@
 #![feature(macro_rules)]
 
 extern crate hyper;
-extern crate debug;
 
 use std::io::util::copy;
 use std::io::net::ip::Ipv4Addr;