Remove extern crate rustc_macros from rustc_middle.

compiler/rustc_middle/src/traits/mod.rs

@@ -20,6 +20,9 @@ use rustc_errors::{Applicability, Diag, EmissionGuarantee};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::HirId;
+use rustc_macros::{
+    Decodable, Encodable, HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable,
+};
 use rustc_span::def_id::{LocalDefId, CRATE_DEF_ID};
 use rustc_span::symbol::Symbol;
 use rustc_span::{Span, DUMMY_SP};