rust: pl011: remove unnecessary "extern crate"

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/hw/char/pl011/src/lib.rs

@@ -25,10 +25,6 @@
 #![allow(clippy::upper_case_acronyms)]
 #![allow(clippy::result_unit_err)]
 
-extern crate bilge;
-extern crate bilge_impl;
-extern crate qemu_api;
-
 use qemu_api::c_str;
 
 pub mod device;