Use String::new() instead of "".to_string()

Co-authored-by: Marijn Schouten <hkBst@users.noreply.github.com>

Author: jackh726

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -2968,7 +2968,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 let r_paren = self.tcx.sess.source_map().end_point(expr.span);
                                 return Some((
                                     vec![
-                                        (box_new.span.to(l_paren), "".to_string()),
+                                        (box_new.span.to(l_paren), String::new()),
                                         (r_paren, "".to_string()),
                                     ],
                                     "consider removing the Box".to_string(),