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/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 {