Show `Foo` instead of `<FooConstForMethod as Foo>` in E0323

[estebank]

Given a file

trait Foo {
    fn bar(&self);
}

pub struct FooConstForMethod;

impl Foo for FooConstForMethod {
    const bar: u64 = 1;
}

produces output

error[E0323]: item `bar` is an associated const, which doesn't match its trait `<FooConstForMethod as Foo>`
  --> $DIR/impl-wrong-item-for-trait.rs
   |
XX |     const bar: u64 = 1;
   |     ^^^^^^^^^^^^^^^^^^^ does not match trait

as per this review from @nikomatsakis, it would make sense to change it so that the output is (at least in this case):

error[E0323]: item `bar` is an associated const, which doesn't match its trait `Foo`

[eddyb]

This seems to me like the difference between {:?} and {} on a ty::TraitRef. That is, all you'd need to do is remove :? from the format string.