qga/vss: use standard windows headers location

qga/vss: use standard windows headers location

Stop using special paths with outdated headers from an old SDK.

Instead, use standard include paths.

You can still build against the old SDK by running configure with
--extra-cxxflags="-isystem /path/to/inc/win2003/"

(this also allows to build against MinGW headers, which are currently
broken as in 9.0)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>