Adjust coherence test to reflect that only the orphan rule prevents you from adding *generalizing* impls

src/test/compile-fail/coherence-cross-crate-conflict.rs

@@ -8,8 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Regression test for #3512 - conflicting trait impls in different crates should give a
-// 'conflicting implementations' error message.
+// The error here is strictly due to orphan rules; the impl here
+// generalizes the one upstream
 
 // aux-build:trait_impl_conflict.rs
 extern crate trait_impl_conflict;
@@ -17,7 +17,6 @@ use trait_impl_conflict::Foo;
 
 impl<A> Foo for A {
     //~^ ERROR type parameter `A` must be used as the type parameter for some local type
-    //~^^ ERROR E0119
 }
 
 fn main() {