Remove extern crate tracing from numerous crates.

compiler/rustc_expand/src/config.rs

@@ -20,6 +20,7 @@ use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
 use thin_vec::ThinVec;
+use tracing::instrument;
 
 /// A folder that strips out items that do not belong in the current configuration.
 pub struct StripUnconfigured<'a> {