doc: Be more specific about how to box closures

Author: richo

src/librustc/middle/ty.rs

@@ -5151,8 +5151,7 @@ pub fn note_and_explain_type_err<'tcx>(cx: &ctxt<'tcx>, err: &type_err<'tcx>, sp
             if expected_str == found_str && expected_str == "closure" {
                 cx.sess.span_note(sp, &format!("no two closures, even if identical, have the same \
                                                 type"));
-                cx.sess.span_help(sp, &format!("consider boxing your closure and/or \
-                                        using it as a trait object"));
+                cx.sess.span_help(sp, &format!("consider boxing your closure as a trait object"));
             }
         }
         _ => {}