Fix clippy::needless_borrow in the compiler

`x clippy compiler -Aclippy::all -Wclippy::needless_borrow --fix`.

Then I had to remove a few unnecessary parens and muts that were exposed
now.

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -97,7 +97,7 @@ pub(super) trait GoalKind<'tcx>:
                 bug!("expected object type in `consider_object_bound_candidate`");
             };
             ecx.add_goals(structural_traits::predicates_for_object_candidate(
-                &ecx,
+                ecx,
                 goal.param_env,
                 goal.predicate.trait_ref(tcx),
                 bounds,

compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs

@@ -50,14 +50,14 @@ pub(in crate::solve) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
 
         ty::Array(element_ty, _) | ty::Slice(element_ty) => Ok(vec![element_ty]),
 
-        ty::Tuple(ref tys) => {
+        ty::Tuple(tys) => {
             // (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
             Ok(tys.iter().collect())
         }
 
-        ty::Closure(_, ref args) => Ok(vec![args.as_closure().tupled_upvars_ty()]),
+        ty::Closure(_, args) => Ok(vec![args.as_closure().tupled_upvars_ty()]),
 
-        ty::Coroutine(_, ref args, _) => {
+        ty::Coroutine(_, args, _) => {
             let coroutine_args = args.as_coroutine();
             Ok(vec![coroutine_args.tupled_upvars_ty(), coroutine_args.witness()])
         }

compiler/rustc_trait_selection/src/solve/inspect/analyse.rs

@@ -175,7 +175,7 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
                 warn!("unexpected root evaluation: {:?}", self.evaluation);
                 return vec![];
             }
-            inspect::CanonicalGoalEvaluationKind::Evaluation { ref revisions } => {
+            inspect::CanonicalGoalEvaluationKind::Evaluation { revisions } => {
                 if let Some(last) = revisions.last() {
                     last
                 } else {