fix few more

warning: this argument is a mutable reference, but not used mutably
   --> compiler\rustc_trait_selection\src\traits\project.rs:511:12
    |
511 |     selcx: &mut SelectionContext<'a, 'tcx>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing to: `&SelectionContext<'a, 'tcx>`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut

warning: this argument is a mutable reference, but not used mutably
   --> compiler\rustc_trait_selection\src\traits\specialize\specialization_graph.rs:201:28
    |
201 | fn iter_children(children: &mut Children) -> impl Iterator<Item = DefId> + '_ {
    |                            ^^^^^^^^^^^^^ help: consider changing to: `&Children`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 3f433a9e919..f9e5dc169de 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -205,7 +205,7 @@ impl Iterator for SupertraitDefIds<'_> {
 /// returning the resulting subject and all obligations that arise.
 /// The obligations are closed under normalization.
 pub fn impl_subject_and_oblig<'a, 'tcx>(
-    selcx: &mut SelectionContext<'a, 'tcx>,
+    selcx: &SelectionContext<'a, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     impl_def_id: DefId,
     impl_args: GenericArgsRef<'tcx>,