remove bogus assertion and comments

The code (incorrectly) assumed that constants could not have generics
in scope, but it's not really a problem if they do.

src/test/run-pass/nll/issue-47153-generic-const.rs

@@ -0,0 +1,27 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for #47153: constants in a generic context (such as
+// a trait) used to ICE.
+
+#![feature(nll)]
+#![allow(warnings)]
+
+trait Foo {
+    const B: bool = true;
+}
+
+struct Bar<T> { x: T }
+
+impl<T> Bar<T> {
+    const B: bool = true;
+}
+
+fn main() { }