Use the new keyboard state tracked for sdl2.  We can drop the modifier
state tracking from sdl2.  Also keyup code is simpler, the state tracker
will take care to not send suspious keyup events to the guest.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20190122092814.14919-4-kraxel@redhat.com