Remove unnecessary attribute

Remove unnecessary attribute

An attribute, NS_ATTRIBUTE_ACCEPTANCE, is removed as the usage has
been changed. Instead the value of MessageID is set to NS_ALLOW(1)
or NS_DENY(2) for the response of subscription.

Change-Id: I48d6b34449602fec9e083620273f991a52ef4bbe
Signed-off-by: ch79.cho <ch79.cho@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/10527
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Uze Choi <uzchoi@samsung.com>