[cleanup] Eliminate obsolete TODOs

Bug: v8:8015
Change-Id: Ic6d3b4f927095ba2e78509c1ba07e5b9258426e2
Reviewed-on: https://chromium-review.googlesource.com/1198182Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55617}

test/debugger/debug/es6/generators-debug-scopes.js

@@ -42,8 +42,7 @@ function RunTest(name, formals_and_body, args, handler, continuation) {
   run(function () { return fun.apply(null, args) });
   run(function () { return gen.apply(null, args).next().value });
 
-  // TODO(wingo): Uncomment after bug 2838 is fixed.
-  // Debug.setListener(null);
+  Debug.setListener(null);
 }
 
 // Check that two scope are the same.