Auto merge of #125105 - nnethercote:rustc_resolve-cleanups, r=estebank

`rustc_resolve` cleanups

Some improvements I found while looking through this code.

r? `@estebank`

compiler/rustc_resolve/src/def_collector.rs

@@ -7,6 +7,7 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_span::hygiene::LocalExpnId;
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_span::Span;
+use tracing::debug;
 
 pub(crate) fn collect_definitions(
     resolver: &mut Resolver<'_, '_>,