usb-redir: Get rid of local shadow copy of packet headers

The shadow copy only serves as an extra check (besides the packet-id) to
ensure the packet we get back is a reply to the packet we think it is.

This check has never triggered in all the time usb-redir is in use now,
and since the verified data in the returned packet-header is not used
otherwise, removing the check does not open any possibilities for the
usbredirhost to confuse us.

This is a preparation patch for completely getting rid of the async-packet
struct in usb-redir, instead relying on the (new) per ep queues in the
qemu usb core.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
