Remove unnecessary .to_string()/.as_str()s

compiler/rustc_parse/src/parser/expr.rs

@@ -3288,7 +3288,7 @@ impl<'a> Parser<'a> {
                         } else {
                             Applicability::MaybeIncorrect
                         };
-                        err.span_suggestion_verbose(sugg_sp, msg, "=> ".to_string(), applicability);
+                        err.span_suggestion_verbose(sugg_sp, msg, "=> ", applicability);
                     }
                 }
                 err

compiler/rustc_parse/src/parser/generics.rs

@@ -148,7 +148,7 @@ impl<'a> Parser<'a> {
             .with_span_suggestion_verbose(
                 mistyped_const_ident.span,
                 "use the `const` keyword",
-                kw::Const.as_str(),
+                kw::Const,
                 Applicability::MachineApplicable,
             )
             .emit();

compiler/rustc_parse/src/parser/item.rs

@@ -1453,7 +1453,7 @@ impl<'a> Parser<'a> {
                                 err.span_suggestion_verbose(
                                     prev_span,
                                     "perhaps you meant to use `struct` here",
-                                    "struct".to_string(),
+                                    "struct",
                                     Applicability::MaybeIncorrect,
                                 );
                             }