Updated other affected tests.

src/test/compile-fail/nll/reference-carried-through-struct-field.rs

@@ -20,7 +20,6 @@ fn foo() {
     let wrapper = Wrap { w: &mut x };
     x += 1; //[ast]~ ERROR cannot assign to `x` because it is borrowed [E0506]
     //[mir]~^ ERROR cannot assign to `x` because it is borrowed [E0506]
-    //[mir]~^^ ERROR cannot use `x` because it was mutably borrowed [E0503]
     *wrapper.w += 1;
 }