Clean up js-test-post.js remainders.

r161289 deleted js-test-post.js, so this CL cleans up.

Review URL: https://codereview.chromium.org/75493002

git-svn-id: svn://svn.chromium.org/blink/trunk@162227 bbb929c8-8fbe-4397-9dbb-9b2b20218538