Delete http/tests/resources/js-test-{pre|post}.js.

Use the one in fast/js. This leaves us with only two copies of these files
left (the others are in fast/js/mozilla and I don't especially see the
need to get rid of that copy).

TBR=eae@chromium.org

Review URL: https://codereview.chromium.org/46393004

git-svn-id: svn://svn.chromium.org/blink/trunk@161284 bbb929c8-8fbe-4397-9dbb-9b2b20218538