fix compile-fail tests

Author: RalfJung

src/test/compile-fail/consts/const-err3.rs

@@ -14,7 +14,6 @@ fn main() {
     //~^ ERROR const_err
     let _e = [5u8][1];
     //~^ ERROR const_err
-    //~| ERROR this expression will panic at runtime
     black_box(b);
     black_box(c);
     black_box(d);