update some compile-fail tests

Some errors, about trait objects not implementing their own trait when
they aren’t object-safe, aren’t being reported. Here is the error
missing from compile-fail/trait-test-2.rs:

```
error[E0277]: the trait bound `dyn bar: bar` is not satisfied
  --> src/test/compile-fail/trait-test-2.rs:20:26
   |
20 |     (box 10 as Box<bar>).dup();
   |                          ^^^ the trait `bar` is not implemented
for `dyn bar`
```

My best guess is it has to do with how object-safety checks now include
trait-solving. It doesn’t look like a very useful error, so I’m not too
worried.

src/test/ui/traits/trait-item-privacy.rs

@@ -110,9 +110,7 @@ fn check_assoc_const() {
     // A, B, C are resolved as inherent items, their traits don't need to be in scope
     C::A; //~ ERROR associated constant `A` is private
           //~^ ERROR the trait `assoc_const::C` cannot be made into an object
-          //~| ERROR the trait bound `dyn assoc_const::C: assoc_const::A` is not satisfied
     C::B; // ERROR the trait `assoc_const::C` cannot be made into an object
-          //~^ ERROR the trait bound `dyn assoc_const::C: assoc_const::B` is not satisfied
     C::C; // OK
 }
 

src/test/ui/traits/trait-test-2.rs

@@ -20,5 +20,4 @@ fn main() {
     (box 10 as Box<bar>).dup();
     //~^ ERROR E0038
     //~| ERROR E0038
-    //~| ERROR E0277
 }