Remove idlharness tests that duplicate existing tests.

[Ms2ger]

• 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.