Remove extern crate tracing from numerous crates.

compiler/rustc_pattern_analysis/src/usefulness.rs

@@ -709,16 +709,15 @@
 //! I (Nadrieril) prefer to put new tests in `ui/pattern/usefulness` unless there's a specific
 //! reason not to, for example if they crucially depend on a particular feature like `or_patterns`.
 
+use self::PlaceValidity::*;
+use crate::constructor::{Constructor, ConstructorSet, IntRange};
+use crate::pat::{DeconstructedPat, PatId, PatOrWild, WitnessPat};
+use crate::{Captures, MatchArm, PatCx, PrivateUninhabitedField};
 use rustc_hash::FxHashSet;
 use rustc_index::bit_set::BitSet;
 use smallvec::{smallvec, SmallVec};
 use std::fmt;
-
-use crate::constructor::{Constructor, ConstructorSet, IntRange};
-use crate::pat::{DeconstructedPat, PatId, PatOrWild, WitnessPat};
-use crate::{Captures, MatchArm, PatCx, PrivateUninhabitedField};
-
-use self::PlaceValidity::*;
+use tracing::{debug, instrument};
 
 #[cfg(feature = "rustc")]
 use rustc_data_structures::stack::ensure_sufficient_stack;