Fixing OCCancel with High_QOS in observe isn't deleting CB.

Fixing OCCancel with High_QOS in observe isn't deleting CB.

(Bug IOT-126) Calling OCCancel should result in deleting all
associated structures including callbacks. This also should
happen when we deregister observation.

Change-Id: I34dd67288873ce27919a12a1d5fe244ef80751b7
Signed-off-by: Yamin Al-Mousa <yamin.s.al-mousa@intel.com>
(cherry picked from commit bd3dd4b91f1bca31402240052199f2557ad1d055)
Reviewed-on: https://gerrit.iotivity.org/gerrit/202
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Sudarshan Prasad <sudarshan.prasad@intel.com>