[IOT-1575] Fixed session delete function to resolve double free issue

[IOT-1575] Fixed session delete function to resolve double free issue

- fix double free issue in tcpserver
  when disconnecting TCP session

Change-Id: Ica0b9f0976426d66309ef7304149eb54489b6b66
Signed-off-by: Hyuna Jo <hyuna0213.jo@samsung.com>
Signed-off-by: Minji Park <minjii.park@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/14495
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: jihwan seo <jihwan.seo@samsung.com>
Reviewed-by: Uze Choi <uzchoi@samsung.com>
Reviewed-by: Jaehong Jo <jaehong.jo@samsung.com>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>