Remove a sample application for group-manager

Remove a sample application for group-manager

APIs for the existing group manager are going to be deprecated and
a functionality to control multiple resources is replaced with one of
scene manager.
Due to this, a sample application for the group manager should be removed.

Change-Id: I3882ab6c2e699d1872154cef5dd25dea73cef89c
Signed-off-by: Jihun Ha <jihun.ha@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/5263
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Habib Virji <habib.virji@samsung.com>