tizen: Remove extlibs git history for gbs export

tizen: Remove extlibs git history for gbs export

Note this is executed just before gbs build,
to allow prepare scripts to use git if needed.

Note:
I noticed an old version of mbedtls is cached on jenkins.

Bug: https://jira.iotivity.org/browse/IOT-1745
Change-Id: I6d28421e2778ca5f6815a450678df3a8e08033e3
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Origin: https://gerrit.iotivity.org/gerrit/#/c/20345/
Reviewed-on: https://gerrit.iotivity.org/gerrit/20345
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Jaehong Jo <jaehong.jo@samsung.com>
Reviewed-by: Dave Thaler <dthaler@microsoft.com>
Reviewed-by: Ziran Sun <ziran.sun@samsung.com>
(cherry picked from commit 5fb0d3438b27afb6a1284bba5e4898c2daed6202)
Reviewed-on: https://gerrit.iotivity.org/gerrit/20343