Rules for use of aria-expanded on native HTML comboboxes

[scottaohara]

Related to #277, but this would be a normative update for input list=.... Update these instances of input list=... to indicate authors are not to use aria-expanded. This is handled by the combobox role and declaring this attribute is both unnecessary, and could potentially lead to misalignment with conflicting native semantics of the native elements.

Furthermore, similar rules would need to be added to the select element when it is exposed as a combobox