Remove extern crate rustc_middle from numerous crates.

compiler/rustc_traits/src/codegen.rs

@@ -5,6 +5,7 @@
 
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::{FulfillmentErrorCode, TraitEngineExt as _};
+use rustc_middle::bug;
 use rustc_middle::traits::CodegenObligationError;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;