IOT-1985: Fixing SimpleClientServer include paths.

IOT-1985: Fixing SimpleClientServer include paths.

SimpleClientServer adds libcoap to its include paths,
which is no longer needed.

Change-Id: I613205e50d1b2f45ae51fa5eed9e036f6d6cc151
Signed-off-by: Pawel Winogrodzki <pawelwi@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18411
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Alex Kelley <alexke@microsoft.com>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>