remove unnecessary to_string and String::new for tool_only_span_suggestion

compiler/rustc_resolve/src/diagnostics.rs

@@ -271,7 +271,7 @@ impl<'a> Resolver<'a> {
                 err.tool_only_span_suggestion(
                     import.use_span_with_attributes,
                     "remove unnecessary import",
-                    String::new(),
+                    "",
                     Applicability::MaybeIncorrect,
                 );
             }
@@ -396,12 +396,7 @@ impl<'a> Resolver<'a> {
         // previous imports.
         if found_closing_brace {
             if let Some(span) = extend_span_to_previous_binding(self.session, span) {
-                err.tool_only_span_suggestion(
-                    span,
-                    message,
-                    String::new(),
-                    Applicability::MaybeIncorrect,
-                );
+                err.tool_only_span_suggestion(span, message, "", Applicability::MaybeIncorrect);
             } else {
                 // Remove the entire line if we cannot extend the span back, this indicates an
                 // `issue_52891::{self}` case.