service/scene-manager: SConscript cleanup

service/scene-manager: SConscript cleanup

This is a scons scripts cleanup left after fixing /W4 warnings for Windows.

Preparing SConscript files for removal of arbitrary global "env"
modifications in script files outside build_common/ directory.

Bug: https://jira.iotivity.org/browse/IOT-1583
Change-Id: Ifc31a5a429f336b4fa17243e65eb5212d6253968
Signed-off-by: Pawel Winogrodzki <pawelwi@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/21151
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Tested-by: Phil Coval <philippe.coval@osg.samsung.com>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>