[IOT-1434] Fix memory leak related server request List.

[IOT-1434] Fix memory leak related server request List.

when there is no response data for virtual reqeust in server.
it should be removed, since it never remove and
causes a big memory leak.

Change-Id: Ic65692ae8b2c1c27f554f466d00bd0cc1674118f
Signed-off-by: jihwan.seo <jihwan.seo@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/12947
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
(cherry picked from commit d54b727a3f55d0238393fd14781e0723df4a9e17)
Reviewed-on: https://gerrit.iotivity.org/gerrit/13057