Bug: Generics error with `--hide-marker-traits`

[Nadrieril]

Reported by @sonmarcho:

//@ charon-args=--hide-marker-traits
#![feature(const_destruct)]
use std::marker::Destruct;
fn drop<T: Destruct>(_: T) {}

gives

fn drop<T>(@1: T)
{
    let @0: (); // return
    let @1: T; // arg #1

    @0 := ()
    @0 := ()
    drop[missing(@TraitClauseBound(0, 1))] @1
    return
}

Note the missing trait ref, caused by removing the Destruct clause.