Remove #[macro_use] extern crate tracing from rustc_middle.

compiler/rustc_middle/src/middle/region.rs

@@ -13,6 +13,7 @@ use rustc_hir as hir;
 use rustc_hir::{HirId, HirIdMap, Node};
 use rustc_macros::{HashStable, TyDecodable, TyEncodable};
 use rustc_span::{Span, DUMMY_SP};
+use tracing::debug;
 
 use std::fmt;
 use std::ops::Deref;

compiler/rustc_middle/src/middle/stability.rs

@@ -23,6 +23,7 @@ use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
 use std::num::NonZero;
+use tracing::debug;
 
 #[derive(PartialEq, Clone, Copy, Debug)]
 pub enum StabilityLevel {