net: skbuff: remove unused HAVE_HW_TIME_STAMP feature define

Remove unused HAVE_HW_TIME_STAMP feature define (introduced by
commit ac45f602 ("net: infrastructure for hardware time stamping").

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>