parser: address review comments

Author: Centril

src/librustc_hir/print.rs

@@ -648,7 +648,7 @@ impl<'a> State<'a> {
                     self.s.space();
                 }
 
-                if let hir::Constness::Const = constness {
+                if constness == hir::Constness::Const {
                     self.word_nbsp("const");
                 }
 

src/librustc_parse/parser/item.rs

@@ -646,7 +646,7 @@ impl<'a> Parser<'a> {
             self.expect_semi()?;
 
             let whole_span = lo.to(self.prev_span);
-            if let IsAuto::Yes = is_auto {
+            if is_auto == IsAuto::Yes {
                 let msg = "trait aliases cannot be `auto`";
                 self.struct_span_err(whole_span, msg).span_label(whole_span, msg).emit();
             }