tizen: Drop TARGET_ARCH from gbsbuild.sh

tizen: Drop TARGET_ARCH from gbsbuild.sh

Instead rely on gbs -a arg to select desired arch

Revert "tizen: Use TARGET_ARCH in samples"

This reverts commit 4be7601cb4b0747132b5ae04ceaeea7541976b93.
https://gerrit.iotivity.org/gerrit/#/c/19055/

Bug: https://jira.iotivity.org/browse/IOT-2032
Change-Id: I4be7601cb4b0747132b5ae04ceaeea7541976b93
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/21099
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>