msxml3: Use the existing READYSTAT type instead of creating our own enum READYSTAT (and mixing the two).

[Nikolay Sivov]

> If there_is_  a reason to keep the two separate, I strongly suggest to
> use different names (having a typedef READYSTAT as well as an enum by
> that name is tricky) and someone needs to look in the mixing of types
> that happens in line 277.
Makes sense, yes. Honestly I didn't check for this type to be defined 
already, and it just happens to use the same name.