Remove extern crate tracing from numerous crates.

compiler/rustc_ast_lowering/src/lib.rs

@@ -37,11 +37,7 @@
 #![feature(box_patterns)]
 #![feature(let_chains)]
 
-#[macro_use]
-extern crate tracing;
-
 use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait};
-
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::ptr::P;
 use rustc_ast::{self as ast, *};
@@ -69,6 +65,7 @@ use rustc_span::{DesugaringKind, Span, DUMMY_SP};
 use smallvec::{smallvec, SmallVec};
 use std::collections::hash_map::Entry;
 use thin_vec::ThinVec;
+use tracing::{debug, instrument, trace};
 
 macro_rules! arena_vec {
     ($this:expr; $($x:expr),*) => (