gccrs: avoid printing to stderr in selftest::rust_flatten_list

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.

OK for trunk?

gcc/rust/ChangeLog:
	* resolve/rust-ast-resolve-item.cc (selftest::rust_flatten_list):
	Remove output to stderr.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>

gcc/rust/resolve/rust-ast-resolve-item.cc

@@ -1202,9 +1202,6 @@ rust_flatten_list (void)
   auto paths = std::vector<Rust::AST::SimplePath> ();
   Rust::Resolver::flatten_list (list, paths);
 
-  for (auto &path : paths)
-    fprintf (stderr, "%s\n", path.as_string ().c_str ());
-
   ASSERT_TRUE (!paths.empty ());
   ASSERT_EQ (paths.size (), 2);
   ASSERT_EQ (paths[0].get_segments ()[0].as_string (), "foo");