remove unnecessary to_string and String::new for tool_only_span_suggestion

compiler/rustc_builtin_macros/src/asm.rs

@@ -363,7 +363,7 @@ fn err_duplicate_option<'a>(p: &mut Parser<'a>, symbol: Symbol, span: Span) {
     err.tool_only_span_suggestion(
         full_span,
         "remove this option",
-        String::new(),
+        "",
         Applicability::MachineApplicable,
     );
 

compiler/rustc_builtin_macros/src/format.rs

@@ -330,7 +330,7 @@ impl<'a, 'b> Context<'a, 'b> {
                                 err.tool_only_span_suggestion(
                                     sp,
                                     &format!("use the `{}` trait", name),
-                                    (*fmt).to_string(),
+                                    *fmt,
                                     Applicability::MaybeIncorrect,
                                 );
                             }