leak during shutdown when /oic/res is observable

[Danielius1922]

Direct leak of 336 byte(s) in 6 object(s) allocated from:
#0 0x7fb0fe3f7e47 in __interceptor_calloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:90
#1 0x55684ef10b63 in _oc_memb_alloc /home/runner/work/iotivity-lite/iotivity-lite/util/oc_memb.c:86
#2 0x55684ef229d2 in oc_ri_add_timed_event_callback_ticks /home/runner/work/iotivity-lite/iotivity-lite/api/oc_event_callback.c:180
#3 0x55684ef33bb1 in oc_set_delayed_callback /home/runner/work/iotivity-lite/iotivity-lite/api/oc_server_api.c:194
#4 0x55684ef433bb in dispatch_process_batch_observers /home/runner/work/iotivity-lite/iotivity-lite/messaging/coap/observe.c:1133
#5 0x55684ef43dfd in add_notification_batch_observers_list /home/runner/work/iotivity-lite/iotivity-lite/messaging/coap/observe.c:1356
#6 0x55684ef43e3f in coap_remove_discovery_batch_observers_by_resource /home/runner/work/iotivity-lite/iotivity-lite/messaging/coap/observe.c:1365
#7 0x55684ef31798 in oc_ri_delete_resource /home/runner/work/iotivity-lite/iotivity-lite/api/oc_ri.c:683
#8 0x55684ef314e7 in oc_ri_delete_all_app_resources /home/runner/work/iotivity-lite/iotivity-lite/api/oc_ri.c:552
#9 0x55684ef33545 in oc_ri_shutdown /home/runner/work/iotivity-lite/iotivity-lite/api/oc_ri.c:1620
#10 0x55684ef24e7a in oc_main_shutdown /home/runner/work/iotivity-lite/iotivity-lite/api/oc_main.c:441
#11 0x55684eea1423 in ApiHelper::stopServer() /home/runner/work/iotivity-lite/iotivity-lite/api/unittest/ocapitest.cpp:399
#12 0x55684eea27ec in TestServerClient::TearDown() /home/runner/work/iotivity-lite/iotivity-lite/api/unittest/ocapitest.cpp:591

Replication steps

• set -DOC_DISCOVERY_RESOURCE_OBSERVABLE_ENABLED=ON
• run apitest