The definition of version_response channel message in Linux doesn't
include version field, so the upcoming VMBus implementation in QEMU
doesn't set it either.  Neither Windows nor Linux had any problem with
this.

The check against this field is redundant because the message is the
response to initiate_contact message containing the specific version
requested, so the response with version_supported=true is unambiguous.

Drop this check and don't rely on the field to be present in the
message.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>