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_mir_dataflow/src/framework/direction.rs

@@ -196,7 +196,7 @@ impl Direction for Backward {
     {
         results.reset_to_block_entry(state, block);
 
-        vis.visit_block_end(results, &state, block_data, block);
+        vis.visit_block_end(results, state, block_data, block);
 
         // Terminator
         let loc = Location { block, statement_index: block_data.statements.len() };

compiler/rustc_mir_dataflow/src/framework/engine.rs

@@ -295,7 +295,7 @@ where
         let mut results = Results { analysis, entry_sets, _marker: PhantomData };
 
         if tcx.sess.opts.unstable_opts.dump_mir_dataflow {
-            let res = write_graphviz_results(tcx, &body, &mut results, pass_name);
+            let res = write_graphviz_results(tcx, body, &mut results, pass_name);
             if let Err(e) = res {
                 error!("Failed to write graphviz dataflow results: {}", e);
             }

compiler/rustc_mir_dataflow/src/framework/lattice.rs

@@ -342,7 +342,7 @@ impl<V: Clone> Clone for MaybeReachable<V> {
     fn clone_from(&mut self, source: &Self) {
         match (&mut *self, source) {
             (MaybeReachable::Reachable(x), MaybeReachable::Reachable(y)) => {
-                x.clone_from(&y);
+                x.clone_from(y);
             }
             _ => *self = source.clone(),
         }