Remove unneeded extern crate

Author: Zoxc

compiler/rustc_driver/src/lib.rs

@@ -1,7 +1,4 @@
 // This crate is intentionally empty and a rexport of `rustc_driver_impl` to allow the code in
 // `rustc_driver_impl` to be compiled in parallel with other crates.
 
-#![allow(unused_extern_crates)]
-extern crate rustc_driver_impl;
-
 pub use rustc_driver_impl::*;