Diagnostics for tuple structs should not mention `::{{constructor}}`

[whitequark]

To reproduce:

struct X(u32);

fn main() {
    match X(0) {
        X { data } => ()
    }
}

This results in:

error[E0026]: struct `X::{{constructor}}` does not have a field named `data`
 --> <anon>:5:13
  |
5 |         X { data } => ()
  |             ^^^^ struct `X::{{constructor}}` does not have field `data`

It seems rather pointless and potentially confusing to add the ::{{constructor}} part.