Remove #[macro_use] extern crate tracing from rustc_mir_dataflow.

compiler/rustc_mir_dataflow/src/elaborate_drops.rs

@@ -11,6 +11,7 @@ use rustc_span::source_map::Spanned;
 use rustc_span::DUMMY_SP;
 use rustc_target::abi::{FieldIdx, VariantIdx, FIRST_VARIANT};
 use std::{fmt, iter};
+use tracing::{debug, instrument};
 
 /// The value of an inserted drop flag.
 #[derive(Debug, PartialEq, Eq, Copy, Clone)]