[XHR] Remove "Conforming script" product class

AFAICT there is exactly one requirement that applies to scripts. The  
requirement not really testable. I don't see the point in having this  
product class.

I suggest removing the product class and replacing the SHOULD requirement  
with something non-normative, e.g.:

    When the argument is provided script writers are strongly encouraged to
    ensure that they have specified (before invoking send()) the
    Content-Type header via setRequestHeader().

If you do this then perhaps the first paragraph in "Conforming user agent"  
needs an update, too; it currently says:

    A user agent must behave as described in this specification in order to
    be considered conformant even when faced with non-conforming scripts.

Perhaps s/ even when faced with non-conforming scripts//.

-- 
Simon Pieters