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/traits/query/dropck_outlives.rs

@@ -48,9 +48,7 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
         // (T1..Tn) and closures have same properties as T1..Tn --
         // check if *all* of them are trivial.
         ty::Tuple(tys) => tys.iter().all(|t| trivial_dropck_outlives(tcx, t)),
-        ty::Closure(_, ref args) => {
-            trivial_dropck_outlives(tcx, args.as_closure().tupled_upvars_ty())
-        }
+        ty::Closure(_, args) => trivial_dropck_outlives(tcx, args.as_closure().tupled_upvars_ty()),
 
         ty::Adt(def, _) => {
             if Some(def.did()) == tcx.lang_items().manually_drop() {

compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs

@@ -108,7 +108,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         match self.evaluate_obligation(obligation) {
             Ok(result) => result,
             Err(OverflowError::Canonical) => {
-                let mut selcx = SelectionContext::new(&self);
+                let mut selcx = SelectionContext::new(self);
                 selcx.evaluate_root_obligation(obligation).unwrap_or_else(|r| match r {
                     OverflowError::Canonical => {
                         span_bug!(