resolve: Avoid some unstable iteration 2

compiler/rustc_resolve/src/macros.rs

@@ -323,7 +323,6 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
     }
 
     fn check_unused_macros(&mut self) {
-        #[allow(rustc::potential_query_instability)] // FIXME
         for (_, &(node_id, ident)) in self.unused_macros.iter() {
             self.lint_buffer.buffer_lint(
                 UNUSED_MACROS,
@@ -576,7 +575,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         match res {
             Res::Def(DefKind::Macro(_), def_id) => {
                 if let Some(def_id) = def_id.as_local() {
-                    self.unused_macros.remove(&def_id);
+                    self.unused_macros.swap_remove(&def_id);
                     if self.proc_macro_stubs.contains(&def_id) {
                         self.dcx().emit_err(errors::ProcMacroSameCrate {
                             span: path.span,