Remove idlharness tests that duplicate existing tests.

* The idlharness tests are a subset of html/dom/interfaces.html.
* The 'x in document.createElement(script)' tests don't do anything, and
  would duplicate the idlharness test if they did.
* The initial value of script.async is tested in
  html/semantics/scripting-1/the-script-element/async_001.htm.
* The initial value of script.defer is tested in
  html/dom/reflection-misc.html.
Merge pull request #9 from Ms2ger/idlharness

Remove idlharness tests that duplicate existing tests.